In a way it has to be a two pronged approach.  On one hand, you must realize and accept that the Chinese concept of "lies" is not the same as we westeners have.  For them some lies are excusable, or not really lies.

And second, you have to impress to them that you do not like or enjoy lies, and that when you hear one, you loose respect for whomever tell lies.  You will also have to emphazise that you understand the differences in culture, and while you would not mind too much if she continues with her ways with others, at least to you it should not be any more lies.  Explain to her the importance of "trust" in a relationship, and the fact that lies destroy that trust.  Hopefully, with time, she will understand you and she will be motivated to be more truthful to you.  But do not expect a change overnight either, must be patient.

I would have to agree with HappyExPat. You have to ask yourself, "Is the honesty issue the hill I want to die on?" For those who do, perhaps they really should consider not getting in a relationship with a Chinese, or Asian person. The first thing one must realize is, it will happen. I don't think the practice is ultimately designed to decieve as westerners would understand the concept, but a lie is told in the mindset of being non-commiting, or remaining flexible. I have found that mostly, it is in reference to time or activity.

Secondly, for a westerner like myself, I can't sweep the issue under the rug, for a variety of reasons, but when it happens, I don't "blow up" everytime it happens, because that encourages the behavior of being more secretive.

It is a process, where two people learn to adopt the measurments of each other's culture and discover those things that are important to each other. For me, absolute honesty is one of the most important things about trusting another person, and I've approached it like that. Trust is built upon knowing that someone will be truthful about the small things in life, which leads to trusting them with the big things. Most Chinese build mental compartments, segmenting "important" things from "trivial" things, and while your partner would never consider cheating on you (important), they would never think twice about telling you a time for being home and showing up a few hours later (trivial). They seriously fail to see the connection between the two (Incidently, when I was in Africa, the regards to time were quite similar).

Approaching it from this angle shows not only the need, but also the necessity of building trust into the foundation of the relationship. If the Chinese partner wants to continue to lie regularly and with immunity, perhaps they should really reconsider whether or not a foreigner is the right choice for a relationship or marriage. Most Chinese have never even thought about this issue before, because it is so deeply rooted in their culture as husbands and wives (some, not all) lie to each other all the time.

The proof of sincerity is whether the practice continues after the other person knows it bothers you badly, or do they try to change (little by little) and become more reliable with not only their answers but also their time. In other words, it has to be judged by the direction they are going in.

And on your part, patience and longsuffering...

Lying is never a problem. The only "chinese" thing she does that is F*cking annoying is she won't accept blame for her screw ups. 

Sure they lie to their partners, but I dont think they lie any more than other cultures. Usually its not a bold faced lie... but something moronic or (as nevermind said) accepting blame for anything regardless how obvious it is.

For a example of moronic. I was at my gfs home for spring festival, and I wanted to sleep with my feet hanging off the bed (kang- the heated bed thing) because Im tall. She said I couldnt because my head would be close to the window. I said that its ok, i wont get a cold. She said that she heard from her coworker of a guy who slept close to the window and his face was crooked after...hahaha. I said "that is the stupidest thing you have ever said. Do you really think that is true?" She wouldnt admit anything. Just said that that was what her coworker said

....needless to say, i had to sleep diagonally so my head wouldnt hang off

Relationships are built on trust and trust is built on truth. We all lie sometimes, those little white lies but I do believe between partners in a serious relationship, married or not, that truth is the only way. When I first met my wife on the internet and we were getting past the initial friends stage I made it clear to her that my belief is that we should always be honest. I have never had reason to doubt anything she has ever said to me, we have now been married over five years, and she did live with me in England for four and a half years so she absorbed the western culture in this respect. However she is trying to help her sister find a boyfriend and some of the things she wanted to post on the profile for the website were not exactly honest in my opinion. I did make it clear to her that she was potentially storing up trouble for her sister by not being totally honest and she did come round to accepting what I said. As other answers here have noted the thing of lying to save face is so deeply ingrained it can affect all parts of the persons life unless you are very carefull. My wife knows that I will not accept lies from her, not even tiny ones and she does accept this but I have caught her saying things to her friends sometimes that I know are not right. We knew where we stood on this issue virtually from day one, so we are fine. If I had someone telling me small lies my trust in that person would be gone and so would I.

I'm trying to think, to be honest my wife doesn't lie to me, she just doesn't take blame for any wrong, she only accepts responsibility for every good thing that has happened while we've been married. Lies are going to happen, no person is without them. I'm a lawyer so I actually get paid to lie, everyday. So if my wife want's to tell a white lie then so be it, I'm not going to harp on that, but larger lies like infedility or money laundering, well I'll accept money laundering but the latter would be devestating