The invention belongs to the technical field of biological engineering, and provides a chitosanase high-yield producing strain, a liquid and solid fermentation method for preparing chitosanase with high activity by using the strain, and chitosan oligosaccharide production method by using the chitosanase. The chitosanase producing strain in the invention is identified as a strain of Bacilluscereus with a strain code of JBSH-003 by 16SrDNA identification, and has a preservation number of CGMCCNo.6129 in China General microbiological culture collection center. The strain can be applied to the production of chitosan to obtain chitosan oligosaccharide with high content, molecular weight range of 1500Dalton-2500Dalton, and relatively concentrated molecular weight range.