Abstract: The causes and solutions of high crutch pressure generated by paraplegia patients in sit-to-stand (STS) movement with lower-limb exoskeleton assistance are studied. In order to explore the relationship between ankle stiffness and crutch pressure, a human-exoskeleton coupled dynamic model is established, and the crutch pressure is introduced as an external force. An exoskeleton STS movement verification experiment is designed to verify the importance of ankle stiffness for reducing crutch pressure. By adjusting the ankle stiffness of a walking assistance exoskeleton named "AIDER", the subjects' average loss energy and the changes of the sole pressure center during the entire STS movement are observed. The results show that the subjects' average loss energy is reduced by 45.18% and the stability is improved by 34.99% after adjusting the ankle stiffness. It is verified that a proper ankle stiffness can effectively reduce the subject's pressure on crutches during STS movement assisted by the lower-limb walking assistance exoskeleton.