The invention provides a preparation method for a polyimide composite material for an automobile. The method comprises the following steps that 1, impurities in sisal fiber are removed, the sisal fiber is dried and added into a sodium hydroxide solution to be soaked, the sisal fiber is taken out to be washed to obtain alkalified sisal fiber, a silane coupling agent is dissolved into an acetic acid solution, the PH value is adjusted to be 7 through ammonium hydroxide, conditioning fluid is obtained after standing, and the alkalified sisal fiber is added into the conditioning fluid for ultrasonic dispersion and taken out for drying, taking, dispersion and smashing to obtain modified sisal fiber; 2, talcum powder is added into a mixing machine to be stirred, then a titanate coupling agent is added, and modified talcum powder is obtained after taking out and drying are performed; 3, polyimide, the modified sisal fiber and the modified talcum powder are added into a stirring machine for stirring and mixing and then taken out to be put into a mold for compression molding forming, and mold stripping is performed to obtain the polyimide composite material for the automobile. According to the preparation method, raw materials are cheap and easy to obtain, the production cost is saved, and the obtained composite material has the good mechanical performance, has the certain degradability and is environmentally friendly.