Abstract: In order to measure the beyond-line-of-sight (BLoS) communication and radar detection performance of a multiple-input multiple-output (MIMO) system in maritime environment with an evaporation duct, a scheme for estimating the capacity of BLoS channel based on the parabolic equation (PE) theory is presented. Based on the two-dimensional scalar wave equation, a two-dimensional PE theory is derived, and the Feit-Fleck PE is solved by combining the split-step Fourier transform (SSFT) algorithm to predict the fading characteristics of the wave propagation in the evaporation duct channel. The corresponding MIMO channel model is established with related statistical laws, then the calculation scheme of channel capacity is deduced. Firstly, the propagation loss distribution in the evaporation duct is simulated, and the path loss in the duct layer and the signal blind area at the same distance is calculated and compared with it in a free space. The feasibility and advantages of BLoS propagation in evaporation duct are verified. In addition, the channel capacity of the system corresponding to different antenna numbers is simulated to quantify the performance improvement of BLoS propagation brought by using MIMO. The results show that the MIMO system in an evaporative duct can effectively improve the channel capacity and achieve better BLoS propagation effect. The results of this paper are of great significance for the application and performance evaluation of MIMO technology in the field of BLoS maritime communication.