Rehabilitation robots joints often require good variable stiffness characteristics to adapt to the compliance of the human body. According to the joint muscle characteristics of the upper limb, the stiffness demands of different positions in the circle trajectory of the upper limb rehabilitation training were analyzed. On this basis, a novel passive variable stiffness actuator was designed. Change of resistance moment by cam-roller-reed mechanism, so as to realize the stiffness change of different positions in the training process of upper limb circumference trajectory. The mathematical model of passive variable stiffness device was established, and the accuracy of the model and the feasibility of the design scheme were verified by software simulation and experiment. Passive variable stiffness actuator realizes the stiffness change in the process of upper limb rehabilitation training. The structure is simple and does not need additional drive and control.