Injection molding is the most widely used process for producing plastic parts.In this process, an important issue is to predict and optimize the warpage before manufacturing. In this paper, a simulation with MOLDFLOW software is proposed to optimize the injection molding process. The optimization process aims at minimizing the warpage of the critical injection molding part in which process parameters, gate location and its shape are the design variables. Moldflow Plastic Insight software is used to analyze the warpage of the injection molding part. The mold temperature, melt temperature, injection time, packing pressure and packing time are regarded as process parameters. The results shown that to reduce warpage in plastc part not only the process parameters should be optimized but also effect of gate shape and especially its position should be considered in precise parts. Moreover the results shown that moldflow injection molding simulation software is able to accurately predict the part warpage, but it doesn’t consider the viscoelastic behaviour of plastic material in process.