Abstract: Heterogeneous network with full-dimensional (FD) multiple-input multiple-output (MIMO) can effectively improve the transmission rate by developing vertical dimensions; however, it can cause the signal leakage and decrease the system's physical layer security performances. In this paper, using the beamforming to eliminate the interference in the downlink of the heterogeneous network, we propose an analysis method with stochastic geometric theory to obtain the closed-form expression of the secure connection probability on the legitimate users. The secure connection probability is related to the density of heterogeneous network small cell base stations (BSs). Simulation results verify the correctness of the safety connection probability, and determine the density value of heterogeneous network BS in a given scenario.