Abstract: Warpage deformation easily occurs in guide rails of vehicle storage boxes during the injection molding process. This paper reported an analysis and a modification method for the local warpage of the guide rail on the basis of its injection-molding characteristics. Using a Moldflow software for numerical simulation, the orthogonal design method was adopted to deduce the optimal process parameters for the injection molding of the guide rails by using polyoxymethylene as a raw material. In this orthogonal design, mould temperature, injection time, packing pressure and cooling time were taken as experimental factors, and the warpage deformation was taken as an experimental target. The guide rail was injection-molded with these optimized process parameters, and its warpage was controlled with 0.5 mm in the x and z directions. This result well met the requirement of production.