In recent years, with the continuous upgrading of terrorist activities, the application of imaging radar has expanded to the detection of hidden targets, such as target detection:behind the wall, mine detection, dangerous object imaging in security inspection, etc. With the development of application requirements, radar imaging has gradually expanded from two-dimensional (distance azimuth) to three-dimensional (distance azimuth altitude). Three dimensional imaging can overcome the shadow effect and spatial blur of two-dimensional imaging. It is widely used in through wall, security inspection and other scenes. Based on the traditional BP imaging algorithm, this paper studies the near-field 3D imaging algorithm suitable for MIMO radar, and verifies the feasibility and effectiveness of the algorithm through simulation experiments.