Abstract: Objectives:  In order to study the influence of information fusion of different depth on the accuracy of the navigation system composed of MEMS inertial navigation system (M-INS) and global navigation and positioning system (GNSS), and to achieve indoor and outdoor integrated positioning.   Methods:  First, based on the factor graph optimization algorithm (FGO), a loosely coupled system of M-INS/single-point GNSS and a tightly coupled system of M-INS/pseudo range/Doppler velocity are established respectively, and the advantages of the tightly coupled design are verified by experiments. Then, the visual inertial odometry (VIO) factor is inserted into the factor structure of the tightly coupled M-INS/GNSS system in a loosely coupled manner, and a tight- loosely coupled multisource fusion algorithm model based on FGO is proposed. Finally, the positioning accuracy and indoor and outdoor integrated positioning capability of the system are verified by experiments.   Results:  The main experimental results are:1) when four satellites cannot be observed and the single-point positioning solution cannot be obtained, the positioning accuracy of the M-INS/GNSS tightly coupled system can reach twice that of the M-INS/GNSS loosely coupled system; 2) In the case of the sudden failure of either GNSS or VIO, the FGO-based M-INS/GNSS/VIO tight-loosely coupled system can continue to provide reliable positioning, and the average errors of the east and north directions are improved by 53.98% and 54.74% respectively compared with the M-INS/GNSS/VIO system based on the filtering method.   Conclusions:  Experimental results show that:1) compared with the loosely coupled M-INS/GNSS system, the M-INS/GNSS tightly coupled system effectively reduces the impact of GNSS signal instability on the system, and has higher accuracy and robustness; 2) The proposed tightly-loosely coupled system can seamlessly respond to changes between indoor and outdoor environments, significantly improving the ability of indoor and outdoor integrated positioning of the system.