Using the calculator technique forecast factor selection, equation establishment and sample fitting into a composite ensemble are integrated，and the forecast factor selection and manmachine conversation platform by building forecast equation are established. This platform has three modules, i.e. document information module, factor primary election module and regression analysis module, which can be described as follows:（1）The document information module is mainly reading the forecast the object document and forecast factor document, examining and displaying the consistency of information length in file header； （2）The factor primary election module is mainly calculating the weather factor or physical quantity field’s correlativity between each of grid point factors and the amount of forecast field, and through analysis of this correlation field the combination factors are finally found out； （3） The regression analysis module is carrying on stepwise regression towards forecasting object and combination factor which has picked up from the equation by the second module， and then the forecasting equation is build up, and according to the regression equation’s parameter and the rate of sample fitting and through changing the standards for picking up and getting rid of regression results are adjusted.