Avermectin is susceptible to oxidation and photolysis, resulting in instability under UV irradiation and a short half-life. To solve this problem, many materials have been used to prevent the photodegradation of avermectin, but the complexity of the preparation process, the difficultly in biodegradation and the residual organic solvents, hinder their practical application. Fortunately, PDA emerged with negligible toxicity, environmental friendliness, extraordinary biocompatibility, and good adhesion, and it is widely used, especially as an UV-shielding material, which implies its huge potential in pesticides as a preferred candidate to melanin but this has never been reported. Herein, a gentle and flexible approach to the preparation of PDA coated avermectin was developed, to protect avermectin from photodegradation, through the oxidation self-polymerization of dopamine. The thickness of the polymer coating was controlled using a multistep deposition technique. The as-prepared products were used to study the effects of the coating thickness on the controlled-release and the UV-shielding property for avermectin. The results showed that the release rate of avermectin could be tailored using the thickness of the PDA layer. Most importantly, the PDA coating exhibited remarkable UV-shielding properties for avermectin, and the UV protection of the PDA layer for avermectin was improved with the coating getting thicker. Therefore, the system has a promising future in practical applications, so as to achieve sustained release and prevent the photodegradation of pesticides.