<p>Most current passive exoskeletons assist a single movement task, and it remains a challenge to design exoskeletons for multiple movements to further reduce human metabolic rate. In this paper, a passive knee-ankle exoskeleton is designed based on the geometrical laws of the human knee and ankle joints angle changes during walking and squatting. It utilises extension springs installed between the knee and ankle joints to store and release energy during motion, thereby assisting walking and squatting. The AnyBody Modelling System(version 7.4.4, AnyBody Technology A/S, Aalborg, Denmark) is used to establish a coupled human-exoskeleton model to simulate walking and squatting tasks, and to compare and analyse key indices such as metabolic rate, joint work, and muscle activity for biomechanical verification. The simulation results show that the passive knee-ankle exoskeleton reduces the metabolic rate by 5.87% and 7.66% during walking and squatting tasks, respectively. Additionally, it reduces the total work done by the knee-ankle joints by 7.52% and 9.91%, and significantly reduces the muscle activity of the major lower limb muscles. These results demonstrate the effectiveness of the designed exoskeleton in assisting walking and squatting tasks. This study may provide new ideas for the design of other exoskeletons to assist multiple movements in the future.</p> Graphical Abstract <p></p>