The number of people with a mobility disorder caused by stroke, spinal cord injury, or other related diseases is increasing rapidly. In order to improve the quality of life of these people, devices that can assist them to regain the ability to walk are of great demand. Recently, brain-controlled lower limb exoskeletons release the burden of therapists and provide effective and repetitive gait training. In the past decade, robot assistive devices such as exoskeletons have made great progress, and some products have been commercialized. Brain-controlled lower limb exoskeleton is a wearable robot system that integrates human intelligence and robot power. The basic concepts of brain control of the lower extremities exoskeleton are introduced. Several main applications of the brain controlled lower limb exoskeleton in gait rehabilitation were summarized, and the action intention of the wearer and the technology of Electroencephalogram(EEG) signal processing were evaluated. The extensive application, limitations, future research and development direction of the lower limb exoskeleton developed at the present time are discussed.