Degradable resin- coated controlled release fertilizer is one of the hottest current research focuses in the field of fertilizer. In terms of practical application, the photodegradability characteristics of three kinds of coatings including polyethylene/hydrophilic nano-TiO2 composite, polyethylene/hydrophilic nano-TiO2 composite and pure polyethylene were analyzed under irradiation of sunlight and ultraviolet by ATR-FTIR, which was aimed to know their degradation behaviors under two conditions. The result showed that under irradiation of sunlight and ultraviolet, the type of functional group was not changed with the addition of the photo-catalyst, but the photo-catalyst just had an effect on intensity of functional groups. The trend was polyethylene/hydrophobic nano-TiO2 composite>polyethylene/hydrophilic nano-TiO2 composite>pure polyethylene. Furthermore, sunlight and ultraviolet had different effects on molecular structures of coatings. Under irradiation of sunlight, crosslinking reaction took place and ether bond was generated among the carbon chain of polyethylene except for the form of hydroperoxides. Then, carbon chain continued being oxidized to form carbonyl group. The existence of carbonyl group promoted the further degradation of coatings; under irradiation of ultraviolet, high local concentrations of reactive oxygen species were produced and the ability to attack the carbon chain of polymer was strong. Thus, the long alkyl chain of polyethylene was quickly oxidized to form intermediate products containing carbonyl groups. However, the irradiation experiment of ultraviolet didn’t fully reveal the degradation behavior of coatings.