Objective To calculate joint torques and muscle forces of astronaut in spacesuit by establishing the biomechanical simulation model of upper limb interaction for human-spacesuit system, so as to assess the risk in extra-vehicular activities. Methods For spacesuit upper limb, the kinematic model of rigid body rotation and hysteresis model of joint resistant torque were built, respectively, to describe the kinematic and dynamic features of spacesuit joints. Kinematic coupling of human and spacesuit upper limb was fulfilled by restricting the displacement between spacesuit elbow and human elbow, and dynamic coupling was fulfilled by using virtual reaction element. An integrated simulation model was established in the framework of inverse sport biomechanics. With this model, the elbow flexion/extension of the astronaut under pressure-suited, unpressured-suited and unsuited condition was simulated for case study. Results The correlation coefficients of predicted muscle activation and iEMG for biceps under the three conditions were 0.86, 0.71 and 0.65, respectively; the corresponding correlation coefficients for triceps were 0.75, 0.61 and 0.60, respectively. The consistency between predicted muscle activations and surface electromyography collected in experiment qualitatively validated the accuracy of this model, and the consistency between human elbow joint torque working on muscles and spacesuit elbow joint resistant torque validated the rationality of the model. Conclusions The established biomechanical simulation model of upper limb interaction for human-spacesuit system can effectively calculate the joint torque and muscle force of astronaut in spacesuit. The simulation and experiment results indicate that joint resistant torque in pressured spacesuit has great influence on human joint torque and muscle workload, which offers methodological support for physical workload and musculoskeletal risk evaluation for astronauts in extra-vehicular activity.