Abstract: In order to effectively prevent the spread of Bursaphelenchus xylophilus disease, the toxicity of different concentrations of Beauveria Bassiana spore suspension to the 4th instar larvae of Monochamus alternatus was compared to select the optimal concentration. On this basis, Beauveria bassiana protease, chitinase and lipase were used as synergistic agents to test their synergistic effect on B. bassiana virulence, and the best synergistic enzyme was screened out by comparing the mortality rate of M. alternatus larvae. The results showed that 1×10⁸cfu/ml spore suspension had the highest toxicity to the 4th instar larvae of B. bassiana, and protease solution was the best synergistic agent for B. bassiana toxicity. In this study, it was proved that adding enzyme synergist to B. bassiana preparation could improve the insecticidal effect and provide a theoretical basis for the control of borers.