Aiming at the problem of autonomous obstacle avoidance of UAV (unmanned aerial vehicle) in complex dynamic environment, an improved speed obstacle method was proposed to improve the autonomous obstacle avoidance ability of UAV in complex environment. Firstly, according to the principle of velocity obstacle method, a mathematical model was constructed to determine whether there was conflict between UAV and dynamic obstacle. Then, the adaptive safety distance was added and the Kalman filter was used to predict the position of the dynamic obstacle at the next moment, and a velocity obstacle area was reconstructed. Finally, an improved dynamic window method was used to solve the optimal obstacle avoidance strategy for the feasible obstacle avoidance region. The feasibility and effectiveness of the proposed algorithm were verified by the simulation experiments of different scenes and multiple obstacles.