I have a US citizenship. My Chinese passport will expire in two years. I know dual citizenship won't work. I'm considering renouncing my US citizenship in order to renew my Chinese passport. Will China regard me as a non-citizen even if I give up my US citizenship, therefore not renewing my passport? Bottomline question: was it game over as far as my Chinese citizenship goes the moment I became a US citizen? Will giving up US citizenship help nothing in Chinese government's eyes?
If by China you mean the People's Republic of China, Article 9 of the PRC Nationality law says that a PRC citizen residing abroad who voluntarily acquires a foreign nationality automatically loses PRC nationality. It is automatic, so yes, the moment you naturalized, your PRC nationality was gone. It doesn't come back just because you renounced your other nationalities. It doesn't matter if your passport is unexpired -- you cannot use it as a proof of nationality anymore. Article 13 supposedly says that foreigners who were once PRC nationals could apply to regain PRC nationality if they have a legitimate reason, and if approved, cannot retain foreign nationality; but I am not sure if there is a procedure to do this in practice.
If by China you mean the Republic of China, ROC nationality is not automatically lost upon acquiring a foreign nationality, and you should be able to get / renew ROC passports with no problem.
Also, keep in mind that applying to renounce US citizenship costs a lot in fees, may subject you to expatriation tax, and can only be done at a US consulate outside the US.