The communication and networking system with intelligent reflective surface (IRS) can effectively improve security and spectrum efficiency. Unmanned Aerial Vehicle (UAV) is widely used to increase the coverage and flexibility of the network. The integration of IRS and UAV is expected to enable flexible, energy-efficient, and secure communication networks. In this paper, an IRS-assisted UAV network is considered, \boldsymbol the UAV equipped with one IRS serves as a passive relay. Our main problem is to maximize the secrecy rate of the system through jointly optimizing the UAV location and phase shifts of the IRS. To solve this problem, an iterative algorithm is proposed, \boldsymbol the UAV location is optimized with fixed phase shifts and the phase shifts are optimized with updated UAV location. The numerical results show that the proposed design can achieve a good secrecy performance.