The invention relates to a preparation method of a beta-Ga2O3/SiC nanometer composite material, and solves the problems of large particle diameter, complex preparation process and long reaction time of the traditional method. The preparation method comprises the following steps: 1, adding urea to deionized water, heating and stirring till the urea is completely dissolved, then adding a Ga(NO3)3 solution, and stirring till a colorless transparent solution is obtained; 2, transferring into a container with a polytetrafluoroethylene lining, then placing the container into a microwave digestion furnace for heating, and after reaction is finished, naturally cooling to room temperature to obtain a gamma-Ga2O3 precursor; 3, dropwise adding the gamma-Ga2O3 precursor to SiC, and then firstly drying moisture through microwave evaporation and then carrying out microwave heat treatment to obtain an SiC-containing solid mixture; 4, adding the SiC-containing solid mixture to the deionized water for centrifugalization, and then carrying out vacuum drying to obtain the beta-Ga2O3/SiC nanometer composite material.