To solve several problems in mold design of irregular cover plastic parts, taking an electrical appliance cover as an example, CAE technology was adopted to compare molding effects of three gating system schemes：single point gate, double point gates along X direction and double point gates along Y direction, cooling analysis was conducted to test effect of cooling system with baffled hole system in moving mold side and simple cooling hole in fixed mold side. Single point gate scheme was selected. For problems found in analysis such as uneven shrinkage and excessive stress, by changing local thickness of plastic part model, adjusting molding process parameters such as mold temperature, filling time and packing curve, optimize layout of cooling system, qualified plastic parts were obtained. With CAD software NX and MoldWizard plug-in , mold structure was constructed including main parting surface, inclined plane positioning between mold working parts and place chambers, dowel lifters, ejecting mechanism combining ejector sleeve for small hole and ejector pins for main body of plastic part, standard 3-plate mold base and standard parts. Efficiency of mold design and test was improved.