VIO-SLAM (Visual Inertial Odometer Simultaneous Localization and Mapping)means that mobile robots use cameras and IMUs as external sensors to build external maps while positioning themselves.This paper reviews the VIO-SLAM positioning system from such modules as the front-end visual inertial navigation odometer, back-end optimization, loop detection and the mapping.As to the visual inertial navigation odometer, the similarities and differences between the feature point method and the optical flow method, and the process of IMU pre-integration are stated.Back-end optimization mainly points out how to deal with the noise in VIO-SLAM process and the bias of the gyroscope and acceleration in IMU.Loop detection mainly expounds how to solve the problem of position estimation drifting with time.In the mapping part, several main mapping methods and strategies are given according to the purpose of mobile robots.Finally, the development trend and prospect of VIO-SLAM are given.