The present invention relates to a plant pesticide preparation method, which comprises: taking 15.4-26.6 parts of garlic, cutting into small particles, flipping for 15-20 min in air, adding 6.8-9.9 parts of edible vinegar essence, grinding the obtained mixture into a vinegar essence garlic puree slurry, taking 29.4-39.7 parts of allium cepa, cutting into small blocks, grinding into a slurry, uniformly mixing the allium cepa slurry and the vinegar essence garlic puree slurry, taking 2.4-4.6 parts of coptis chinensis, crushing, leaching for 2-5 h with water, filtering to remove the residue to obtain an extraction liquid, adding the extraction liquid to the allium cepa-garlic vinegar essence slurry, uniformly stirring, standing for 15-20 days, and filtering to remove the residue to obtain the finished product. According to the present invention, the edible plants are adopted as the raw materials, and the plant pesticide has characteristics of plant disease and insect pest prevention-control and plant nutrition supplement integrated effect, no pollution, no residue, high efficiency, less consumption, and no off-drug period.