A method of quantitative precipitation forecasts for short-range ensemble forecast is presented aiming at inability of ensemble average method to extreme weather event.This method firstly determines ensemble similitude by stepwise aggregation to define the influencing radius of members forecast fields,then determines the weight coefficient of every member according to the similitude degree of one member to other members.It takes into account both the ensemble otherness of members and probability distributing of precipitation.Examination proves that this method improved the forecasting of extreme weather events.This method needn't history data and can accommodate to the change of members so it is prone to operate.