Abstract: The coating materials of slow release fertilizers were prepared by polymerization reaction between polyvinyl alcohol (PVA) and epoxy resin, and their structures were characterized by infrared ray. The water absorption of coatings was measured by the immersion test to determine the optimal modification scheme. In order to study the effect of coating materials, the nitrogen release of coated urea was investigated by a soil incubation method, and the effects of two coated fertilizers (LP40 and HP) are compared. The results show that etherification modified PVA is synthesized by reaction between epoxy groups and hydroxyl, which reduces the amounts of hydroxyls and the water absorption of the modified films. In deionizer water of 202℃, the water absorption of the modified film is 1152 g/kg, which is markedly reduced 884 g/kg compared with the pure PVA films. The concentration of PVA is 70 g/kg, the addition of epoxy resin is 25 g/kg（by mass of PVA solution）, the reaction temperature is 60℃, and the reaction time is 2 hours, the modified film leads to lower water absorption. The coated fertilizer HP is effective to decrease nitrogen release, but the slowrelease is poor compared with the LP40.