The plastic mobile was taken up product as an example. The plastic melt flow was analyzed and simulated by moldflow software，and the mold was designed by the adoption of UG software according to the basic process of modern mold design method，which leads to reasonable injection molding parameters and the optimized mold structure．Compared with the traditional mold design method，the modern mold design method enhances the accuracy of the design and shortens the cycle of the mold design and manufacture，thus is more efficient and economical．