Abstract: In order to solve the problem of dense deployment of user-centric small base stations in fifth generation/beyond the fifth generation(5G/B5G) networks, a three-layer heterogeneous network model with user cluster distribution was constructed. The network model consists of macro base stations (MBS), pico base stations (PBS) and femto base stations (FBS). Stochastic geometry theory is used to model the deployment of base stations in the three-layer heterogeneous network。Fully analyzed the network interference statistical characteristics of the femto base station layer based on SSA interference management, considered the two cases of ordered FBS and Non-ordered FBS, and gave the coverage probability of FBS downlink. Through simulation, the correctness of the theoretical results is verified, the influence of coverage radius, variance and macro base station density on coverage probability is analyzed, and it is concluded that the ordered FBS and the Non-ordered FBS scheme depend on the system parameters in terms of coverage probability.