Abstract: The optimal adjuncts tested were screened based on the effects of adjunct on microbial activities and formulation properties. The wettable powder of Bacillus thuringiensis and Beauveria bassiana was prepared in accordance with formulation standards using a muller mixer to blend B. thuringiensis, B. bassiana and adjuncts. The results showed that the optimal ratio of B. thuringiensis and B. bassiana as a wettable powder in accordance with formulation standards was 3:1, including 1% Morwet EFW, 3% SDS, 9% Morwet D425, 9% TERSPERSE 2020, 0.3% xanthan and carrier to 100%. The suspension percentage, conidia germination and average particle size were 72.73%, 75.13% and 13.76 m, respectively, and the wetting time for the formulated material was shorter than 1 min. Every parameter of the wettable powder formulations of B. thuringiensis and B. bassiana was in accordance with formulation standards. The wettable power formulations containing both B. thuringiensis and B. bassiana had higher insecticidal efficacy to Malacosoma neustria testacea than wettable powder formulations containing B. thuringiensis or B. bassiana alone. Therefore, the wettable powder of B. thuringiensis and B. bassiana is environment- friendly pesticide with high insecticidal activity and long persistence.