In order to achieve the long-term management of endometriosis, a more economical and environmentally friendly material, ethylene vinyl acetate (EVA), was used to prepare a intravaginal ring with anastrozole (ATZ). This paper has compared the pharmacokinetic parameters with oral tablets (Aida®) in mini pigs and evaluated the uterine targeted effect and mucosal irritation of the ring. A bioassay method was developed and validated for the determination of ATZ in mini pigs. The determination of ATZ was achieved by LC-MS/MS using terfenadine as the internal standard. Separation was achieved on a Kinetex-C18 110A chromatographic column (3 × 30 mm, 2.6 μm; Phenomenex) with a gradient mobile phase consisting of methanol (0.1% formic acid) and water (0.1% formic acid). The method has been proved to be scientific and sensitive through methodological validation and can be easily and quickly applied to the determination of the content of anastrozole in mini pigs. The pharmacokinetic test results show that there was no significant difference in pharmacokinetic parameters between the two formulations. The intravaginal ring has a passive targeting effect on the uterus, and its mucosal irritation is acceptable. The intravaginal ring provides a new method for long-term management of endometriosis.