Mobile networks have experienced a tremendous growth in data volume and user density due to the coexistence of a large number of users and devices.Deploying small basic station(SBS)within the coverage area of macro base station(MBS)and caching popular content in SBS in advance is an effective means to provide high-speed and low-latency services in next-generation mobile communication networks.Aiming at the unstable heterogeneous net work environment and the difficulty of finding an accurate mathematical model for optimisation,a collaborative edge caching algorithm for heterogeneous networks based on transmission delay minimization is proposed.Firstly,a new user mobile location prediction method is given based on Markovian mobile prediction model,considering the influence of user social relations on user mobility.Secondly,multi-agent deep deterministic policy gradient(MADDPG)algorithm is used to reduce the content delivery delay and improve the cache hit rate by user association,delay control and cache design.Simulation results show that compared with traditional DDPG and greedy algorithms,the cache hit rate is improved by 17.89%and 42.71%,and the content delivery delay is reduced by 9.07%and 12.86%,respectively,which can effectively solve the resource allocation and cache design problems in heterogeneous networks.