Due to the social aging process, an increasing number of patients are experiencing lower-limb injuries caused by diseases or accidents, which makes the rehabilitation of their exercise ability particularly important. Compared with the traditional physical rehabilitation method, the lower-limb rehabilitation robot can more accurately evaluate and greatly improve the effect and efficiency of rehabilitation, thereby saving medical rehabilitation resources. Lower-limb rehabilitation robots comprise intelligent bionic mechanical and electrical equipment based on developments in the fields of rehabilitation medicine, mechanics, control, robotics, computer science, artificial intelligence, and many others. These robots are mainly categorized as either sitting/horizontal or standing lower-limb rehabilitation robots, according to the patients' rehabilitation posture. The sitting/horizontal lower-limb rehabilitation robot can be further divided into the pedal and exoskeleton types, and the standing lower-limb rehabilitation robot is divided into the suspension weight-loss robot and independent wearable robot. In this paper, we investigate several representative products involving lower-limb rehabilitation robots that are widely used around the world. Key technologies related to the active and passive degrees of freedom, driving mode, transmission joint, sensing technology, motion control strategy, and training mode of lower-limb rehabilitation robots are analyzed in detail. The typical clinical test cases of various robots are compared and discussed, and future technological developments are forecasted.