Abstract: Aimed at the problems such as low power density, slow attitude response and easy to be interfered by heavy load current of the traditional four-rotor UAV, a mechatronics four-rotor UAV is designed. The STM32 main control chip, Mahony complementary filtering algorithm and double closed-loop cascade PID control are adopted to improve the accuracy of UAV attitude calculation and control timeliness. The UAV power module has the functions of charging, display and detection. The design of power partition, filtering and fault protection separates the power supply from the main control chip, which improves the system reliability. Multi-sensor design realizes UAV attitude acquisition. The hardware debugging results show that the designed UAV has good dynamic response performance and practical value.