Robotic lower limb prosthesis and lower limb exoskeletons play an important role in assisting people with limb disabilities to recover daily activities. Electromyography (EMG)-based direct volitional control is the key step towards adaptive and autonomously control. To solve this problem, the research progress on human lower limb motion intention mapping based on surface EMG signals was addressed including proportional EMG control, musculoskeletal model and artificial intelligence, and the key challenges faced by them were discussed. At last, existing challenges and future directions were discussed.