The invention relates to a cross-linked starch sizing agent for chitosan fibers as well as a preparation method and application of the cross-linked starch sizing agent. The preparation method comprises the following steps: adding starch, sodium hydroxide and anhydrous sodium carbonate into deionized water for pre-gelatinization and gelatinization, cooling, slowly dropwise adding a crosslinking agent solution and then carrying out vacuum defoamation treatment, thus obtaining the cross-linked starch sizing agent for sizing the chitosan fibers. The sizing agent is prepared by processing the following raw materials in parts by weight: 10 to 58 parts of starch, 0.5 to 15 parts of a crosslinking agent, 1 to 1.5 parts of sodium hydroxide, 6 to 10 parts of anhydrous sodium carbonate and 250 to 300parts of water. Starch sized chitosan fibers are prepared by soaking the chitosan fibers into the sizing agent, uniformly sizing, drying and crosslinking at 45 to 50 DEG C, wherein the breaking strength of the starch sized chitosan fibers is improved by 60.7 to 83.7 percent relative to the chitosan fibers. The preparation method disclosed by the invention is simple in technology and low in cost;the sizing method improves the mechanical strength of the chitosan fibers and has a broad application prospect.