In designing the Band-pass filter of parallel coupled microstrip lines with egual width by using cascade methed,some parameters should be adjusted many times and the results should be validated repeatedly thus causing some difficulties in determining the optimum parameters.To counter this problem,the combination of an improved genetic algorithms and the cascade method is presented in this paper.The optimal parameters can be obtained,by using the combinative method,through single computation and without adjustments.At last the validity of the method is verified through an example.