The invention discloses a tomato insecticide and a preparation method thereof. The tomato insecticide comprises the following compositions in parts by mass: 30-50 parts of herba andrographis, 20-30 parts of blumea riparia, 10-12 parts of pericarpium granati, 8-10 parts of herba portulacae, 3-5 parts of radix angelicae dahuricae, 20-30 parts of fructus xanthii, 2-4 parts of a material with a Chinese name of Lazipi, 30-40 parts of herba houttuyniae, 8-10 parts of herba ephedrae, 18-20 parts of geraniumwilfordii maxim, 12-14 parts of radix rhapontici, and 1750-1950 parts of water. The tomato insecticide is a plant insecticide, and has the advantages of being green, environment-friendly, free of harm to human and animals, free of drug resistance and the like.