Automobile trim cover's plastic parts are not only required highly in appearance, but also erected with many tiny gussets and other complicated structures, and it is difficult to control the injection and moulding defects such as sink marks, buckling and deformation, makes the design of product die structure and moulding process rather tough. Based on CAD/CAE technology and through simulation and analysis in the influences of gusset thickness on moulding quality, the range of buckling and deformation of the product had been obvious influenced by the of gusset thickness, but without positive correlation. Sink marks would be obviously caused by the larger gusset thickness. When the thickness was 1 mm, the minimum value of sink marks would be 0.02 mm. The molding parameters were optimized by using the comprehensive balance method, which made the maximum warpage of product decreased by about 25%. Then by Fibonacci method, sub-sectional pressure maintaining and optimization were conducted. Through iterative calculus and standard convergence for 8 times, the ideal pressure maintaining parameters were obtained and the maximum range of deformation continued to reduce about 37%, making the rage of buckling and deformation of the final product satisfied with technical requirements. A set of optimization methods for the molding process parameters of the injection molding parts with complex reinforcing plate was presented. The production practice proves that the method is simple and practical, which not only solves the problem of the shrinkage marks and unmanageable warping deformation, but also reduces development cycle and costs. In addition, it provides a reference for similar product.