The invention relates to a preparation method and application of a ternary heterojunction photocatalyst. The method comprises the following steps: respectively preparing Zn(CH3COO)2.2H2O solution andan NH4VO3 solution, under magnetic stirring, dropwise adding the NH4VO3 solution into the Zn(CH3COO)2.2H2O solution to obtain mixed liquor, continuously stirring for a first preset time, transferringinto a reaction still, heating to first preset temperature at a first preset heating rate, then performing microwave hydrothermal treatment for a second preset time, naturally cooling, performing suction filtration to obtain a first pre-polymer, washing with deionized water and absolute ethyl alcohol, putting into a vacuum chamber for drying at second preset temperature for a third preset time, putting into a muffle furnace, heating to third preset temperature at a second preset heating rate, and preserving heat for a fourth preset time to obtain the ternary heterojunction photocatalyst. The catalyst has a good catalytic decomposition function, improves a degradation effect, and meets practical application needs.