Aiming at the problem that the narrow beam cannot be matched in real time due to the relative motion of the transmitter and receiver in the millimeter-wave （mmW） communication system of unmanned aerial vehicles （UAVs）， a three-dimensional （3D） beam tracking method based on unscented Kalman filter （UKF） is proposed. Firstly， the elevation and the azimuth angle of the beam at the receiver and the transmitter are regarded as the state vector of the system， and the sampling point set is obtained by the unscented transform （UT）. Then， the state prediction value and the measurement prediction value are calculated according to the sampling point set. On this basis， the state vector is updated according to the calculated Kalman gain to obtain the optimal estimate of the state vector. Simulations show that the proposed method can improve the beam tracking accuracy of UAV in 3D dynamic environment.