In the process of radar data acquisition, limited amount of information can be provided to postprocessing interpretation by the data acquisition method of single-input and single-output, however, the location and physical parameter information of geological body can be obtained more accurately by using Multi-Input Multi-Output (MIMO) antenna with multiple transmitters and multiple receivers. Especially when collecting borehole radar data and the aperture is very narrow, but the antenna is required to be able to ensure better results in a larger frequency band, therefore, the size of the antenna will be greatly challenged. Meanwhile, the close arrangement of multiple transmitting and receiving antennas will inevitably affect the signal radiation. Based on the borehole radar, this paper simulates and optimizes the Single-Input Multi-Output antenna (SIMO antenna) , the size of which meets the aperture requirements, using HFSS antenna simulation software, and explores the factors affecting the antenna return loss and isolation. Among them, the radius of the dipole has little effect on the return loss and isolation, whereas increasing the number of receiving antennas or increasing the transceiver distance will significantly affect the antenna coupling, with a significant reduction in the amplitude of isolation.