This paper aims to study the effect of free trade zones on regional economic growth. With provincial panel data from 1995 to 2018, the differences in differences (DID) method is used to evaluate the economic growth effect arising from the establishment of free trade zones. The synthetic control method is further used to test the regional heterogeneity of the economic growth effect in the free trade zones. The research results indicate that: first, free trade zones promote the regional economic development significantly and continuously, and the role in promoting is gradually enhanced with the longer time of establishment; second, the test results of the influence mechanism indicate that free trade zones mainly promote economic development by means of trade expansion and foreign investment attraction, and the way to promote economic growth through the optimization and upgrading of the industrial structure has not been brought into full play; third, regional heterogeneity exists in the economic growth effect of free trade zones. Free Trade Zones in Shanghai, Guangdong and Fujian play a significant role in promoting regional economic growth; however, the economic growth effect of Tianjin Free Trade Zone is not obvious.