The invention discloses a preparation method of a carbon-based molybdenum sulfide selenide composite material. Thiourea is respectively dissolved in water, and a thiourea water solution is obtained bystirring; sodium molybdate is dissolved in the water, and a sodium molybdate water solution is obtained by stirring; a selenium powder is dissolved in hydrazine hydrate for ultrasonic dispersion to obtain a selenium powder hydrazine hydrate mixed solution; then after the thiourea water solution, the sodium molybdate water solution and the selenium powder hydrazine hydrate mixed solution are mixedevenly in a beaker, a carbon material is added and transferred in a high-pressure reactor for solvent thermal reaction, airtight reaction is conducted for a period of time, and washing and vacuum drying are conducted after cooling to the room temperature; and an obtained product is annealed in a tube furnace under protection of nitrogen, and the carbon-based molybdenum sulfide selenide compositematerial is obtained. According to the preparation method, a lithium ion diffusion path is advantageously shortened and electrode reaction is advantageously enhanced; and the preparation method is lowin cost and simple in process, by creating vacancies reaction sites are increased, and battery performance is advantageously improved.