The correlational coefficient between the number of the equivalent torrential rain day and the total rainfall at June～August of this century in Beijing is 0.97. The correlational coefficient between the regional average number of the equivalent torrential rain day and the regional average total rainfall is 0.94. The linear correlation between the number of the equivalent torrential rain day and the total rainfall is given by the regression equation and the scatter diagram. The root mean square error of the total rainfall calculated by the regression equation is near 10 percent. The method of the total rainfall calculated by the number of the equivalent torrential rain day can be applied to the operational use.