Multiple-input multiple-output (MIMO) technology is a key technology in 5G mobile communication. MIMO technology refers to multiplying the capacity and spectrum utilization of the communication system without increasing the system bandwidth. MIMO antenna has also become an important part of wireless communication under such a background, and it has become an important research object in the academic environment. This paper mainly designs, simulates, analyzes and studies how to realize the miniaturization and high isolation of MIMO antennas. In this paper, a three-band folded IFA antenna is designed, the characteristic mode of the design model is analyzed, and the placement of the antenna is determined. The coupling between the antennas is reduced by means of defective ground and increased capacitance.