Aiming at the problem of information freshness in unmanned aerial vehicle （UAV） assisted content distribution system， a UAV caching and trajectory optimization algorithm based on age of information （AoI） is proposed to alleviate the problem of long time unanswered user requests in hotspot areas. The problem of minimizing the average cost of accessing the requested content for all users is established by optimizing the ground user clustering， the UAV caching policy and the trajectory within the limited cache capacity and coverage of the UAV. The radius of coverage of UAVs is used as the radius of clustering， and the affinity propagation （AP） clustering algorithm is used to cluster the ground users. The UAV caching problem in this paper is transformed into the 01 backpacking problem， which is solved using the dynamic programming （DP） algorithm. UAV flight trajectories are solved by the genetic algorithm （GA）. Simulation results show that the algorithm proposed in this paper can effectively reduce the average cost for users to obtain the requested content.