Abstract: Abstract: The flat fan nozzle is the most common type of nozzle for various boom sprayers. From the perspective of reducing damage and improving activity, in order to screen the nozzle pattern and spray pressure suitable for spraying microbial pesticide in flat fan nozzles, the comparative experiments of bioactivity damage were carried out for extended range fan nozzle XR, wide-angle fan nozzle TT and air suction fan nozzle AI. The nozzle atomization test system was used to test the droplet distribution of three different spray samples of Bacillus thuringiensis, Brassica californica polyhedrosis virus and water. The influence of nozzle structure and spray pressure on the activity damage of bacteria and virus biological pesticide was quantified by spore germination rate of Bacillus thuringiensis and mortality of Plutella xylostella. The experimental results showed that the XR series fan nozzles with a single direction of flow had less impact on the biological activity than the TT series with multiple flow mutations and the AI series fan nozzles with interference from external air flow. When the XR11002 nozzle sprayed microbial pesticide, the fluid flew through the 2 channels of the same flow direction to the nozzle hole, and there was no sudden change of the fluid direction and no external airflow interference during the spraying process. However, the TT11002 nozzle forcibly changed the direction of the liquid, forcing the fluid to entered the horizontal mixing chamber from the vertical direction, and then changing from the horizontal flow channel to the almost vertical orifice channel, resulting in microbial damage caused by shear stress and normal stress. The AI11003 nozzle was provided with a front hole, and in the hole, the air was sucked into the nozzle due to the Venturi effect. The gas and liquid mixed flow structure caused the microorganism to be subjected to multiple interferences and force, causing damage to biological structures. At 0.5 MPa, after 16 hours culture, the spore germination rate of Bacillus thuringiensis sprayed with XR11002 sprinkler was 83.76%, while that of TT11002 and AI11003 were 65% and 68.33% respectively. Pressure on the bacterial and viral biological pesticide activity difference was obvious. The pressure had a negative correlation to the activity damage of bacteria, and had no obvious effect on the damage of the virus activity, it was mainly related to the structure of bacteria and virus. The bacteria had the cell structure, the increase of pressure caused the increase of damage degree to cell wall and cell membrane, resulting in the decrease of the living bacteria and subalgebra. The virus had no cell structure, its genetic material was wrapped in the protein shell, and the destruction of the shell did not affect the virus activity. The damage degree of nozzle to virus biologic pesticides was less than that of bacteria, which was caused by the different structure of the 2 organisms. Therefore, when using the flat fan nozzle to spray the microbiological pesticide, the XR series fan nozzle was preferred. Therefore, when using the flat fan nozzle to spray the microbiological pesticide, the XR series fan nozzle was preferred. From the angle of reducing the activity damage, it was suggested that the spray pressure of XR11002 and TT11001 were not greater than 0.15MPa, and the spray pressure of AI11003 was not greater than 0.3MPa. In combination with various factors, when spraying microbial pesticides with fan nozzles, XR11001 in XR series fan nozzles was preferred from the viewpoint of droplet distribution and activity, and the spraying pressure was 0.15 MPa. In the spraying of virus pesticides, the impact of the type of nozzle and pressure on the viral activity damage can be ignored. This paper provides a reference for screening the optimal nozzle type and spraying pressure suitable for bio-pesticide spraying.