Upper limb rehabilitation robot can effectively help patients recover motor ability. Existing rehabilitation robots are usually driven by rigid motors and the mechanical structures cannot adapt to the different patients with the different physical parameters and different rehabilitation needs. This paper designs a reconfigurable upper limb rehabilitation exoskeleton for elbow and wrist joints driven by pneumatic muscle actuators (PMAs). The exoskeleton can assist patients to achieve elbow flexion/extension, wrist flexion/ extension and adduction/abduction by integrating soft elbow and wrist joint modules which can work separately or together. The wrist joint can realize two degrees of freedom (2-DoF) movement via adjustable modules. To conquer the dynamic model errors and load disturbances when reconstructing the modular joints, a non-singular fast terminal sliding mode control method based on nonlinear disturbance observer (NFTSMC-NDO) is proposed, and a position/force hierarchical control method is formed to ensure the controllability of the soft modular robot. Experimental results show that the proposed method can achieve high-precision motion control of soft modular joints and provide reconfigurable assistance for patients, improving the adaptability and compliance of rehabilitation training.