The invention provides a preparation method of a thermal conductive film based on a graphene polyimide composite sponge precursor. The preparation method comprises the following steps that a grapheneoxide water solution is mixed with a polyimide precursor solution to obtain a graphene oxide/polyamide acid mixed solution, then the graphene oxide/polyamide acid mixed solution is frozen to obtain agraphene oxide/polyamide acid frozen sponge, a frozen drying method is adopted for drying to obtain a graphene oxide/polyamide acid composite sponge, the graphene oxide/polyamide acid composite spongeis placed in a hot pressing reactor, hot pressing oxidizing pre-processing is adopted and machinery pressuring is conducted to obtain a reduced graphene oxide/polyamide acid composite film, then vacuum hot processing and machinery pressuring are adopted to obtain a graphene/polyimide carbon film, then the graphene/polyimide carbon film is placed in a high-temperature graphitization furnace, and agradient temperature rising method is adopted to achieve graphitization of the carbon film. According to the technical scheme of the preparation method, the problem of dispersion of graphene is improved, the obtained film has a certain flexibility and high mechanical strength, and has better electrical and thermal conductivity, and the preparation technology is simple.