A water-soluble and biodegradable antimicrobial agent is provided, comprising a polymer composed of a segment A and a segment B, in which, the segment A has the following formula I:the segment B has the following formula II:wherein the segment A and the segment B in the polymer have a molar ratio of 1:0.007-1.2, and n is 0 or 1, m is an integer of 0-2, m+n≠0, X is H, Na, K, NH4, ½Ca, or ½Mg, and Y is Cl, Br, or I.