The invention provides a preparation method of an automotive blended composite material. The preparation method comprises the following steps that 1, silicon carbide crystal whiskers, gamma-mercaptopropyltrimethoxysilane and ethyl alcohol are mixed, stirred, filtered and dried; 2, bisphenol A-type polycarbonate is dried; 3, polyhydroxyalkanoate and linear low-density polyethylene are dried; 4, thecomponents are mixed, ethylene-glycidyl methacrylate, ethylene-methyl acrylate-glycidyl methacrylate, n-butyl stearate, talcum powder, gum wood powder and oleamide are added, and mixing is performedin a high-speed mixing machine; 5, the mixture is added into a double-screw extruder for extrusion and mixing, and grain-sized dicing is performed after cooling; 6, drying is performed in a vacuum drying oven; 7, injection molding is performed to obtain the material through an injection molding machine. The automotive blended composite material prepared by adopting the preparation method of the automotive blended composite material has very good mechanical properties and has good tensile strength, high elongation at break and good bending property and meanwhile has very good shock resistance performance.