Since the adoption of reform and opening-up policy with high speed development of china's economy the gap of the three sections of china (west， centre section and east) arouses broad attention. The empirical analysis by calculating GDP pei capita， GDP/Weighted Coefficient of variation and banding together the indexes of given time and period gives the cause of the economy gap of the three areas and proves that economy gap of the three areas presented " S "shape and not the "Reversed U" shape which Simon Kuznets mentioned.