Developed from Adam Smith’s Comparative Advantage theory, the Synthesis Comparative Advantage theory focuses on the multi-factor and synthesis comparative advantage, including the exogenous and the endogenous comparative advantages, instead of the single factor and exogenous comparative advantage. Through an empirical study of the agricultural comparative advantage with the panel data of 31 provinces in China from 2000 to 2007, the paper has proved the existence of comparative advantage and the importance of endogenous comparative advantage.