Abstract: In order to improve the communication quality of users in the coverage area of UAV base station in multi-cell millimeter wave system, a flight attitude optimization scheme of UAV base station is proposed in this paper. In this scheme, the throughput is optimized when the number of UAV base station antennas tends to infinity, and the asymptotic expression of the maximum throughput is obtained, and then the throughput optimization problem is further refined into the antenna tilt angle optimization problem. Finally, the antenna array tilt angle to maximize the throughput is obtained by exhaustive search algorithm, and the UAV flight attitude is optimized by adjusting the antenna tilt angle. Numerical simulation results show that the proposed optimization scheme can effectively improve the system performance and has theoretical significance for the performance optimization of multi-cell UAV millimeter wave communication system.