Abstract: Traditional channel models cannot be used for UAV millimeter wave (mmWave) communication scenarios directly, by using the ray tracing theory, a three-dimensional (3D) geometry-based stochastic channel (GSCM) model for UAV mmWave communications is proposed. The updating algorithm of time-variant channel parameters is also developed and it considers the time evolving process of propagation parameters, i.e., communication distance, signal angles, path delay and power. Meanwhile, for the propagation scenario of Nanjing University of Aeronautics and Astronautics campus, we analyzes the statistical properties of our proposed model such as time delay distribution, delay spread distribution, angle distribution and angle spread by simulation method. Simulation results demonstrate that the proposed model can reproduce the non-stationarity of fading channels and the simulated statistical properties agree well with the measured ones, which indicates its usefulness of the system design, performance optimization and evaluation for UAV mmWave communication systems.