The invention discloses a preparation method of a ZnSnO3@rGO composite material. The preparation method comprises the following steps: 1) adding a dried graphene sheet and potassium permanganate intoa strong H2SO4/H3PO4 mixed solution respectively, stirring at a constant temperature of 50 DEG C for 12 hours, cooling to room temperature, adding the reaction solution into ice containing 30 percentof H2O2, filtering after the color of the mixture changes to luminous yellow to obtain graphene oxide, washing with hydrochloric acid to remove metal ions, and performing vacuum freeze drying for 24 hours; 2) adding the prepared graphene oxide into a beaker filled with deionized water, performing ultrasonic treatment for 24 hours, adding SnCl4.5H2O and Zn(NO3)2.6H2O which are equal in molar mass respectively, performing magnetic stirring, adding 24 percent by weight of ammonia water into the reaction mixture dropwise, continuously stirring till the pH value is 9, heating the mixed solution ata temperature of 130 DEG C for 15 hours, washing with distilled water and ethanol respectively to obtain black powder particles several times, and drying the black powder particles to obtain a ZnSnO3@rGO composite material. The prepared composite material has the advantages of small thickness, good wave absorbing effect and wide absorbing wave band.