The invention relates to a preparation method of a biopesticide wettable powder and application thereof in sclerotiniose prevention and treatment on crops such as oilseed rape and sunflowers and belongs to the technical field of biopesticides. The biopesticide wettable powder provided by the invention is prepared from conithyrium minitans conidial powder prepared through solid fermentation as an effective component together with certain amounts of carriers and aids. The biopesticide wettable powder is applied into soil by using a pre-burying method, and is capable of effectively preventing andtreating sclerotiniose of economical crops such as oilseed rape and sunflowers.