The invention discloses an anionic ultraviolet radiation-resistant water-soluble additive and a preparation method thereof. The preparation method comprises placing an organic anti-UV aid and diisocyanate in a reactor, adding butanone and a catalyst into the reactor, carrying out stirring for a reaction, carrying out separation to obtain an intermediate, putting the intermediate into the reactor,adding a compound containing a -OH reactive group and a -COOH group or a compound containing a -NH2 reactive group and a -SO3Na group into the reactor, adding butanone and a catalyst into the reactor,carrying out a reaction process and when the added compound contains a -OH reactive group and a -COOH group, adding triethylamine to neutralize so that the carboxylic acid-type water-soluble additiveis obtained or when the added compound contains a -NH2 reactive group and a -SO3Na group, washing the mixture to obtain the sulfonic acid-type water-soluble additive. The water-soluble additive can effectively prevent use of an organic solvent and reduce the environmental pollution.