Aiming at the problem that the plant protection UAV in spraying operations is easily affected by the disturbance factors such as motor dynamic characteristics, body vibration and mechanical friction, a back‑stepping robust control law is designed. Firstly, the mathematical model of plant protection UAV with various disturbance factors was established, and the disturbance size was accurately estimated by the designed expanded state observer. Then, combined with the back‑stepping method, the control commands of azimuth speed, motor current and motor voltage were designed respectively, which improved the flight accuracy of plant protection UAV. Finally, the simulation experiments were conducted to verify that the maximum estimation errors of the designed extended state observer for azimuth angle, azimuth angular acceleration and drive motor current were only 0.03°/s, 0.03°/s2 and 0.04 A/s respectively. The proposed back‑stepping robust control law could make the maximum errors of pitch angle, roll angle and heading angle as only 0.4°, 0.6° and 0.5°. The test results showed that the proposed robust control law could effectively overcome the influence of interference factors such as motor dynamic characteristics, body vibration and mechanical friction, and ensured the precise and stable flight of plant protection UAV and reduced the proportion of re‑spray and missed spray areas to 0.23% and 0.27% respectively.