The photodegradation of three polymer materials was studied, i.e., polyolefin, polyurethane, and a copolymer of styrene, butyl acrylate, and methyl methacrylate (P(St-co-BA-co-MMA) latex). These polymers are mostly used as film-coating materials for producing controlled-release fertilizers. The P(St-co-BA-co-MMA) latex film degraded at the highest rate and the film surface became porous under UV irradiation. The weak cross-link chain in the latex film was broken and the connections between the microspheres were destroyed. A photo-oxidative aging reaction weakened the tenacity of the latex film, which resulted in the easy release of microspheres from the film, leading to a reduction in film thickness and film tensile strength. Threfore, P(St-co-BA-co-MMA) latex is a promising coating material for controlled-release fertilizers.