The Chinese stock market is affected by many factors, stock index as a measure of the overall situation of the stock market plays an important role; therefore, it is essential to study the mechanism of the stock index.In view of the overall status of China's securities market factors, decision of stock index mechanism is studied, using the least square method, stepwise regression analysis and other methods, the use of Excel, such as EViews software programming calculation, factors such as stock index and GDP growth rate, CHIBOR model. And gradually solve the possible existence of multicollinearity, heteroscedasticity and autocorrelation. Finally puts forward policy Suggestions on the shortcomings of China's securities market.