The invention provides a modified-chitosan-containing anti-ultraviolet finishing agent for cotton fabric and anti-ultraviolet cotton fabric obtained by aid of the anti-ultraviolet finishing agent. The modified-chitosan-containing anti-ultraviolet finishing agent for the cotton fabric is a uniformly mixed solution of 3,4,5-trimethoxybenzoyl chitosan, a crosslinking agent, a penetrant and an acetic acid or lactic acid solution, wherein the crosslinking agent is organic polycarboxylic acid or amino-modified silicone oil emulsion; the penetrant is either JFC or peregal O. The anti-ultraviolet cotton fabric with anti-ultraviolet, anti-bacterial and anti-crease finishing functions is obtained through double-dip double-nip, water washing and drying, the anti-ultraviolet, anti-bacterial and anti-crease finishing functions are high in durability, the cotton fabric still maintains the original style of the fabric after finishing, the hand feel, the strength, the whiteness and the color of the cotton fabric are not affected, and the original human body affinity is maintained; the finishing agent is simple in composition and easy to prepare, and a finishing process is simple and environment-friendly.