Abstract: In this paper，the aqueous suspension pesticides were prepared by combining the Spodoptera exigua nuclera polyhedrosis virus（ seNPV） and emamectin benzoate. This combination of biological and chemical pesticides to a certain extent makes up for the shortcomings of expensive and slow-acting biological pesticides. The LC50 of seNPV obtained by feed-dose method was 1.88×105 PIB/mL，and the LC50 of emamectin benzoate was 1.9185 mg/L. Co-toxicity factor was used to evaluate the formulation synergism，and the efficiency range was 80∶1～350∶1. Cotoxicity coefficient method was adopted to screen the optimum ratio of pesticides，and the two agents had the best effect when their volume ratio of LC50 was 200∶1. The synergistic multiple was 0.9841. Through the combination of two methods，the experimental efficiency was improved. The optimized composition method was used to screen the formulation of the SeNPV·mamectin benzoate suspension concentrate formulation. By determining the retention， surface tension and suspension rate of different formulations on the leaves，and performing cold storage and heat storage experiments，the optimum formulation of pesticides was determined to be：seNPV 6.62%，mamectin benzoate 3.38%，sodium lauryl sulfate 6%，p-styrene sulfonic acid 2%，silicone 4%，magnesium silicate aluminum 1%， xanthan gum 0.5%，water to 100%.