In order to obtain a chitosanase high-yield strain, separated and purified Aspergillus cervinus ZJOU-AC1 was used as raw material to carry out cold source plasma mutagenesis and screening, then the single factor and L9(34) orthogonal tests were used to optimize the fermentation conditions of the mutant strain. Through the experiment, the optimal mutation time was set as 90s. The stable mutant strain of Aspergillus cervinus, ZJOU-AC2, was obtained and its chitosanase activity was increased by 50.7% compared with the original strain. The optimum fermentation conditions were as follows: the fermentation temperature was 30℃, the initial pH was 6.0, the fermentation time was 90h and the inoculation amount was 3%. At this time, the chitosanase activity in the fermentation broth was improved by 15.07%.