An insecticide used for garden flower cultivation and a preparing method thereof are disclosed. The insecticide is prepared from, by weight, 16-25 parts of turpentine, 8-14 parts of a compound named as Chinese characters 'Songzhisuantong' by the inventor, 6-11 parts of tobacco leaves, 7-11 parts of hot pepper, 3-5 parts of pirimiphos-methyl, 4-7 parts of mint, 2-6 parts of eucalyptus oil, 15-21 parts of ageratina adenophora, 7-12 parts of a stellera chamaejasme ketone extract and 6-12 parts of lobelia colorata. An effective ratio of the turpentine, the 'Songzhisuantong', the tobacco leaves, the hot pepper, the pirimiphos-methyl, the mint, the eucalyptus oil, the ageratina adenophora, the stellera chamaejasme ketone extract, and the like is adopted to prepare the insecticide. The insecticide and the method are efficient, highly targeted, environment-friendly, free of secondary toxicity, free of pollution, capable of keeping ecological balance and nuisanceless. A formula is reasonable. The preparing process is simple. The natural raw materials are adopted for preparation so that the insecticide has no toxicity, and has no influence on flowers after the insecticide is directly acted on the flowers. Effects are durable, insecticidal effects are good, and the insecticide effects quickly and is convenient to popularize and apply.