I am a U.S. Citizen and have been living abroad for the last year (approx. 350 days) I own a significant portion of a company incorporated in China and work for this company. Thus, I am already paying taxes to China.

Does this mean that I am exempt from paying U.S. federal/state tax (I have no property, bank accounts, etc. in the U.S. although my son is goes to college in the U.S.) under the U.S-China tax treaty to avoid double taxation? Do I still need to file my taxes, and if so, what forms would I need to fill out?

Do I need to report any dividend, interests that I earn in China even if I already paid the appropriate taxes to China? Also, my foreign income is well over what can be excluded with the 2555 form, but once again I have already paid my tax for this in China.

Thank you in advance for any help

If your total worldwide income exceeds the filing requirement, you must file your U.S. tax return.

On your return, you must report your world wide income. If you paid taxes in the foreign country, you will claim credit for taxes paid in the foreign country by filing Form 1116 or can file form 2555 Foreign Earned Income Exclusion..
Read: Your U.S. Tax Return: U.S. Citizen or Resident with Foreign Income

As a U.S. citizen you are taxed on your worldwide income. If you pay taxes to China on that income, you can claim a foreign tax credit to avoid double taxation. You may also be able to claim the foreign earned income exclusion (but you can't claim foreign tax credits on income that is excluded).

You will need to also file Form 5471 for the Chinese corporation ($10,000 penalty for failing to file). You will also need to file Form TD F 90-22.1 if you have foreign bank accounts will balances exceeding $10,000 at any time during the year (significant penalties for failing to file).

You may or may not be required to pay U.S. state income tax, depending on which state you lived in prior to moving to China and depending on other factors.

There may also be other U.S. tax filing requirements, depending on your other activities outside the U.S.