The oil-based suspension of Bacillus thuringiensis is mainly applied to the ultra low volume spraying of mist sprayer and aeroplane,especially apt to control forest pest insect.The result showed,through the test for indexes of the oil-based suspension of Bt on ULV spraying,all indexes accorded with the need of ULV spraying,there are D_(vm)=(85.57?μm)、D_(nm)=115.24?μm,DR=0.74;in field;D_(vmΦ1.2)=74.86?μm,D_(nmΦ1.2)=(60.64?μm),D_(vmΦ0.8)=78.44?μm,D_(nmΦ0.8)=65.43?μm,DR_(Φ1.2)=0.81,DR_(Φ0.8)=0.83,insecticidal effect is (73.75%)～88.82% on 7th day.