A novel fungus strain M3b with high chitosanase activity was screened from the soil of many places to study the specific chitosanase. The morphological observation and 18S rDNA sequence identification of strain M3b were carried out. The single-factor and orthogonal experiments were used to optimize the solid fermentation process for chitosanase produced by M3b. The enzymatic properties of chitosanase purified were investigated. The results showed that strain M3b was Aspergillus tamarii. The optimized fermentation conditions for producing chitosanase produced by M3b based on water as 100% were as follows：1% colloidal chitosan+1% glucose，0.5% ammonium sulfate，bran∶soybean meal=6∶10，inoculation amount 10%，incubation for 6 d，the initial pH 7.0，and the fermentation temperature 32 ℃. Under these conditions，the activity of chitosanase reached 20.56 U/mL，which was 221.3% of the initial fermentation condition. The results of SDS-PAGE and enzyme profiling showed that the strain M3b produced only one chitosanase with a molecular weight of 40 ku. The optimum pH and temperature for the enzymatic reaction of this enzyme was 5.5 and 60 ℃，with the degree of polymerizing the final product obtained by hydrolysis of chitosan≥2. It is indicated that producing chitosanase by solid fermentation of Aspergillus tamarii can significantly improve the activity of chitosanase and reduce the cost of production. The purified chitosanase AtChito40 has stable enzymatic properties，acid and alkali resistance，and can effectively degrade chitosan. It will provide the theoretical and experimental basis for the enzymatic degradation of chitosan and the preparation of chitosan oligosaccharide in industrial production.