Abstract: The Bacillus thuringiensis(Bt) which is considered as the most effective biopesticide ,is widely used in the world, but There were many disadvantages such as low ferment efficiency, narrow spectrum and low biological activity. In order to improve the effectiveness of Bt strain, in this paper, mutagenesis strain-improving of Bacillus Thuringiensis were studied to increase its biological activity. Different methods are as follows. Fiestly, ultraviolet mutagenesis was employed to mutagene the strain. Secondly, the strains were mutagened by DES, nitrous acid. mutagenesis conditions were optimized, The results indicate that the crystal protein were improved by these methods above, particularly through the ultraviolet mutagenesis method, The crystal protein increased by34.2%. The strain with a highly increased crystal protein concentra-tion was obtained.