Abstract: A modified GMDH (Group Method of Data Handling) with multi-input variablegenerators is proposed, in which all input variables of a system can be combined to acttogether on the output. It automatically selects not only optimal partial polynomials, butalso optimal terms in the polynomials. A more meaningful mathematical model and lesstime-consuming for computation can be resulted. Then the dynamic models of grossoutput value of industry-agriculture and national income using the modified GMDHare used to forecast the development of our national economy and to analyse the maineconomic policy of quadrupling.