Abstract: 【Objective】The photolysis of avermectin(AVM)always reduces the effectiveness of its application in agricultural and forest pest control. Here, a simple and economical method was used to improve its photostability.【Method】Ethylcellulose(EC)was employed as the carrier, while methanol was employed as the solvent for this process. AVM and EC were mixed in mass ratios(m_AVM:m_EC)of 1:10, 1:8, 1:6, 1:4, and 1:2 to prepare a series of solutions. Five times the volume of distilled water was then added to the solutions to precipitate the AVM-loaded EC(AVM/EC). The yield, drug-loading rate, photostability, and thermostability of AVM/EC, as well as the utilization rate of AVM, were then determined. Additionally, X-ray diffraction(XRD)analysis was performed to characterize the AVM/EC samples.【Result】The method achieved a shapeless and uniform dispersal of AVM in EC. When the m_AVM:m_EC was increased from 1:10 to 1:6, the AVM/EC yield exceeded 91.85%, while the AVM utilization rate was higher than 81.18%. Additionally, a photodegradation rate of under 15.80% was observed after ultraviolet light exposure for 12 h, and an AVM degradation less than 10.86% was observed. These results were obtained after the AVM/EC was kept at(54 ± 2)℃ for 14 days.【Conclusion】The solvent blending-water addition precipitation method yielded a homogeneous structure of AVM/EC that improved the photostability and thermostability of AVM. Therefore, this method could be a potential approach for the preparation of AVM for incorporation into dosage forms.