The invention relates to a preparation method of self-adhesive pure polyimide composite paper. The preparation method comprises the following steps: under the protection of nitrogen, adding diamine monomers and dianhydride monomers into an aprotic polar solvent for reacting; then, adding a catalyst to perform a polymerization reaction to obtain a polyimide stock solution; filtering, defoaming, diluting, and injecting into a precipitation solution to obtain a polyimide precipitation fibre suspension; washing, filtering and drying to obtain polyimide precipitation fibres; mixing the polyimide precipitation fibres and polyimide chopped fibres to obtain a homogeneous slurry; papermaking, squeezing and drying to obtain polyimide composite paper; performing solvent spraying after-treatment, coldpressing, and drying to obtain the self-adhesive pure polyimide composite paper. According to the preparation method of the self-adhesive pure polyimide composite paper, the solvent spraying after-treatment is adopted, part precipitation fibres are dissolved, and a film-fibre coexisting state is formed after a solvent is removed so that the obtained composite paper has the strength of the film, also has the characteristics of paper, remains original heat resistance, irradiation resistance, electrical performance and the like of polyimide paper, has higher strength, and can meet the application with higher requirement on the environment.