The invention discloses an isaria fumosorosea and abamectin oil suspension agent as well as a preparation method and application of the isaria fumosorosea and abamectin oil suspension agent. The isaria fumosorosea and abamectin oil suspension agent comprises the following components in percentage by mass: 1-5 percent of abamectin, 1-20 percent of isaria fumosorosea fungus powder, 1-20 percent of vegetable oil, 3-15 percent of an emulsifier, 0.1-5 percent of a dispersant, 1-5 percent of a stabilizer, 1-5 percent of a suspending agent, and the balance of mineral oil or methyl oleate. The isaria fumosorosea and abamectin oil suspension agent disclosed by the invention is mainly used for preventing and treating insects including plutella xylostella, solenopsis invicta and the like, has the advantages of synergism, good permeability, high activity, stable effect, long effect lasting period, small environmental pollution, high adhesion, evaporation resistance and the like, also can be used for treating various crop insects, and has quite good application and popularization values.