The invention belongs to the technical field of pesticides, and relates to a pure natural botanical insecticide and a preparation method thereof. The preparation method includes the steps that: S1, fructus cnidii, camphor, tobacco leaves, herba lysimachiae, radix sophorae flavescentis, liquorice and semen strychni are weighed according to the weight part ratio and sequentially put into a grinding machine to be ground into powder; S2, the mixed powder obtained in the step S1 is added into a leaching kettle, water, an emulsifying agent and a dispersing agent are added according to a ratio, heating, and uniform stirring are performed; and S3, after the mixture obtained in the step S2 is cooled, the mixture is put into a centrifugal machine to be subjected to high-speed centrifugal separation, a finished product is collected and put into a chemical agent tank, and the chemical agent tank is closed. When materials are put into a grinding box, the materials cannot be uniformly laid in a grinding seat, as a result, the grinding efficiency is reduced, and the grinding quality of grinding balls on the materials is influenced. With the pure natural botanical insecticide and the preparation method thereof adopted, the above problems can be solved.