Like many countries, China taxes on a progressive scale; the more you earn, the higher percentage of tax you'll have to pay. Taxation rules and regulations applying to you will also be based on your length of stay in the country, so you were quite right to think this would have an impact.
According to this table, as an expat in China for more than 6 months, you fall into the second bracket of tax, meaning all income earned in China will be taxed but any source of income from outside the country isn't taxed in China (an exception or two applies to this rule, which is mentioned in the table).
Hopefully that answers your question? You may also find the Expat Arrivals Banking, Money and Taxes page useful. It is also a good idea to check with an expat tax professional to be 100% sure of your situation. Best of luck with your new venture in China.