A mobile robot localization and perception method for subterranean space exploration is proposed. Firstly, a tightly-coupled LiDAR-odometer-IMU (inertial measurement unit) fusion framework based on factor graph is designed for the problem of structural degeneration in subterranean space. A high-precision IMU/odometer pre-integration model is derived, and the factor graph is utilized to achieve the simultaneous estimation for motion states and sensor parameters of mobile robots. Meanwhile, an object detection method based on LiDAR and infrared camera is proposed to conduct the recognition and relative localization of multiple objects in weak light environment. The experimental results show that the proposed method can improve the positioning accuracy of mobile robots by 50% in structurally degenerated environments and achieve a centimeter-level relative localization accuracy for objects in weak light environment.