Chitosan has the characteristics of biocompatibility, biodegradability, antibacterial activity, and non-toxicity. It is widely used in medicine, pharmaceutical, textile and other fields, but the application of chitosan in the agricultural field is rarely reported. The structural characteristics and functions of chitosan were expounded, and the inhibitory effect of antibacterial agents on plant pathogens and the synergistic promotion effect on biocontrol bacteria were summarized. The applications of chitosan as carrier materials in agricultural fields such as pesticides, fertilizers and soil amendments were introduced, and finally the effects of chitosan on plant immune defense were summarized. The introduction of chitosan to agriculture provides a new type of green material for agricultural producers to improve soil quality and increase agricultural productivity, and offers new ideas on sustainable agriculture.