In China, income tax is based on income received in China (unless you are a China citizen or "permanent" resident ).
Income tax is computed and paid monthly by the payer (and withheld from salary).
In Singapore, generally overseas income is not taxable.
However, check the IRAS website for more complete info:
If you will be spending most of your time in China, you could live comfortably on that income.
It all depends on your lifestyle and expectations.