Aiming at the throughput of Unmanned Aerial Vehicle （UAV） relaying system with multiple user pairs， a UAV assisted amplify-and-forward relaying system was investigated， where a Full-Duplex （FD） fixed-wing UAV employed a Time-Division Multiple Access （TDMA） scheduling protocol to provide relay services for multiple source-destination user pairs. With the goal of maximizing the throughput of the system， a joint optimization problem of communication scheduling， the transmit power and trajectory of the UAV was formulated. Since the optimization variables of the problem were coupled， it was non-convex and hence hard to solve directly. To this end， the initial problem was decomposed into three subproblems corresponding to the optimization of communication scheduling， the optimization of transmit power and the optimization of trajectory of the UAV， respectively. On the basis of solving the three subproblems， an iterative algorithm based on the block coordinate descent technique was proposed to tackle the joint optimization problem by optimizing the three variables blocks alternately. Simulation results demonstrate that the throughput of the joint optimization scheme is at least 6.8% and 79.4% higher than that of two benchmark optimization schemes， respectively.