Abstract: A new method for prediction of torrential rain area is presented.It stand- ardizes those valuses of atmo-physical parameters in the area where it is the most favourable to form torrential rain; Inspects by homologues elsewhere,in all round,the relatively favourable level of producing torrential rain.The level is synthesized and numericalized by the principle of nonlinear mapping,and reflected on to a synoptic chart.Thus a predictional chart of torrential rain area can be located objectively and clearly.In dealing with factors,we used the computer to distinguish and determine the location of jet axis automaticaly by means of the regression analysis.For calculating process,we replace the method of simple relaxational iteration with that of gradient method according to the functional characteristics of the optimum index K,therefore overcome the default that simple relaxational iteration doesn't converge with the number of the sample increased.