The invention relates to a botanical pesticide for controlling crop aphids, and a preparation method for the botanical pesticide. An extracting solution of field sowthistle herb, wormwood and xanthium sibiricum is used as a raw material, and the extracting solution comprises a preservative. According to the botanical pesticide, rhizome and leaves of field sowthistle herb, wormwood and xanthium sibiricum are used as the raw material, and the extracting solution is obtained through juicing field sowthistle herb, wormwood and xanthium sibiricum; then, the extracting solution is diluted with water, and the diluted extracting solution is sprayed to greenhouse crops to play a prevention effect on the crops free of the aphids and to play a well treatment effect on the crops suffering from the aphids. Field trials show that the control effect can reach up to 98.95% or above. The botanical pesticide not only can control the aphids, but also has an obvious prevention and treatment effect on piercing-sucking pests such as spider mites and thrips; in addition, field sowthistle herb, wormwood and xanthium sibiricum are edible and medicinal wild plants, so that during practical use, problems of pesticide residue, environmental pollution and the like can be avoided; as aphid harm is reduced, the yield is increased by 6.35-9.95%.