There aren't any restrictions as such. The difficulty is in the time it takes. You'll need to take your passport, work contract, proof of payments from your employer, tax receipts, and something else I've probably forgotten.
Also, you'll need to exchange RMB for your own currency before sending it. This can be done without actually having to withdraw the money, it just sits in your account.
Make sure you fill out all the forms precisely, cross your fingers and wait for a day or so to see the transfer as having gone through.
Some bank workers will hate you for doing this, so be prepared for a bit of a fight. The whole system is a pain and worth doing as few times as possible.
Dear Kind Poster above,
Perhaps it varies from one area to the other. When I arrived in China in another century, truly, it was just like what you said. Then somewhere over the years, this has all changed. Now, I just take my passport and the amount of RMB that I want changed and I head to the main office of the Bank of China in the city where I live. I had them my passport, the RMB, and in less than ten minutes I receive dollars or euros if they have them (usually not) or pounds (if available). There is a limit, however, of USD 5,000.00 at a time in my city at the Bank of China head branch for one exchange but God knows I have never that limit in one exchange. Otherwise, I just go home and use my ATM card in a Chinese-bank friendly ATM machine, and they do exist, and I can pull out dollars from the account but at less than a favorable rate. Or go to Hong Kong and do the same.
It was so, so cumbersome when I first arrived but that has changed, really it has, at least where I live.
I can also easily wire money overseas up to a certain amount but for that I need a Chinese passport holder, as for the reasons why, don't ask. Here I can use both the Bank of China or the Western Union facilities located in the major China Postal Savings Bank offices.
It will depend on how you will take them out.
If bank or western union or similar, as a foreigner you can only convert the equivalent of $ 500 US dollars per day. If Chinese, no limitation to amount converted daily. Once in dollars, send them out. Or pay here in Rmb and ask for money deliver in local currency there, but the charge is higher. Be aware, wire transfers in China are slower that a molasses IV, at least 10 days. Western Union has a service within 20 minutes there, but also extra. 24 hours is cheaper.
If with you on airplane when exiting China, 6,000 Rmb or equivalent is the maximum legal on you.
Best to ask the airport authorities. Everyone will have a different experience. And will with sincerity offer their advice and opinion, however maybe the reason you are getting varied amounts is because no-one has be stopped and searched. 6 Years past I came from the UK with 50.000 Rmb/Yuan/Quai the equivalent to £5000. I had trouble at the British borders and arrested by police and customs. marched off in front of thousands of people and made to look like a criminal, the money was not concealed, it was in my hand flight bag. After providing proof of how and where I obtained the money [my bank] I was free to go. When I arrived at [HK] Hong Kong I had no trouble I declared the money and continued my travel. However at [GZ] Guangzhou entry and exit station/customs they took it away and said it was limited to 10,000 into and out of the country and the flight information card explained this. I believe now it is around 15 - 16,000. Please check, for they do and will confiscate it as there is a limit to enter and removal of the currency. I guess you take your chances..