Abstract: The gate design for injection molding is crucial.Now, the whole filling process of plastic melting can be simulated by CAE technology quickly and exactly, forecast any possible defect and get it avoided by optimization design.Therefore, CAE provides a reliable reference for mold optimization design and production.In this article, the injection molding process of motorcycle side cover is analyzed by software MoldFlow, and the gate optimization design is conducted.The experimental result shows that a reasonable choice of location, quantity and size of gate not only reduces the deficiencies, such as short injection, gas pocket, warpage, melting-joint imprint effectiveiy, but also ameliorates the filling time, cavity pressure.The actual production becomes more economical and efficient.