A food-grade mosquito larvicide, a preparation method therefor and application thereof. The effective ingredient in the mosquito larvicide is propylene isothiocyanate. The death rate of mosquito larvae can reach 90-100% by 5-50 ppm of propylene isothiocyanate which has higher safety and effect and lower use cost than dithiophosphate. The mosquito larvicide is prepared from the following raw materials in percentage by weight : 1-40% of propylene isothiocyanate, 2-40% of emulsifier, and 20-97% of carrier. A preparation method for the food-grade propylene isothiocyanate mosquito larvicide, comprising a high-pressure homogenizing technology. Proofed by experiments, the mosquito larvicide is diluted by water until the concentration of the propylene isothiocyanate is 5-50 ppm and then is sprayed to the surface of water body, such that the mosquito larvae can be quickly killed. The very important meaning is realized on reducing the pollution number of mosquito larvae and protecting the ecological environment.