The assessment on agricultural support level can reflect the effect of agricultural support policy in a nation. OECD and WTO proposed two methods to measure agricultural support levels and both of them are popular approaches in discussing this topic. This paper compared these two methods and argues the differences between them. The conclusion was OECD’s methods over valued agricultural support levels in developing countries. The study used China as a case to compare the analyzing results by two methods from 2002 to 2012, which proved the conclusion. Recommendations were proposed based on the results for assessment method and policy making for agricultural support in future China.