The plastic planetary gearbox with external gear ring is injection molded with engineering grade POM material, and the tooth surface is precisely ground, with a transmission ≤ 0.05mm. The innovative design of the involute tooth profile structure, combined with the self-lubricating property, can achieve 20000 hours of maintenance-free operation. It is suitable for precision transmission scenarios such as servo motors and robotic joints, with a working temperature range of -30℃ 80℃, and the impact resistance is 40% higher than that of metal gear rings. A standard series with a module of 0.5-3.0 provided, and non-standard customization is supported.