The embodiment of the invention discloses a preparation method for a graphene composite material. The preparation method comprises the following steps that zinc nitrate hexahydrate and a cetyl trimethyl ammonium bromide solution are mixed and stirred at the indoor temperature, a dimethylimidazole aqueous solution is dropwise added in the stirring process, nitrogen-doped graphene dispersion liquidis dropwise added into the above-mentioned solution for the hydrothermal reaction, and the nitrogen-doped graphene composite material loading ZIF-8 is obtained. According to the method, ZIF-8 is loaded on nitrogen-doped graphene in a hydrothermal mode, and the ZIF-8/nitrogen-doped graphene composite material is synthesized. Agglomeration of the ZIF-8/nitrogen-doped graphene composite material is avoided through mutual influence of the ZIF-8 and the nitrogen-doped graphene, the adsorption capacity of the ZIF-8/nitrogen-doped graphene composite material is improved, and therefore the extractionperformance of the ZIF-8/nitrogen-doped graphene composite material is improved.