Since you didn't mention it in your question, I would say that the procedure depends on if your spouse is Chinese or Foreigner.

1) if your spouse is Chinese: you can change your Z working visa by applying to a resident permit (for family reunion). You will then get a visa and resident permit at the same time for a period of one year (2 years if you have a child with foreign passport) with multiple entries.
However, make sure to ask what kind of documents you and your spouse need to provide, because it can be a nightmare to renew it, especially if your spouse's hukou is different than the city she is working in.

2) if your spouse is foreigner: you can change your Z working visa into a resident permit providing your spouse is working. Otherwise, if your spouse's visa was linked to yours, then you can only apply for a tourist visa.

In both cases, it is considered illegal to work in China. However, I think (I cannot bet on this issue) that if you provide services (for instance translation) to companies or people located outside of China and that you get your payments received overseas you can work as independent.

Thanks Sangoku,my wife is Chinese,she lives in same city as family book or Hukou,as we already have a child with British passport, your saying i can apply for 2 year staythanks for advice

If you "applying to a resident permit (for family reunion)" you won't be able to work, frankly speaking having a Z visa or foreign expert certificate is better, as for working you answered it yourself, you can't (well you can but it's illegal)...