Upper limb assistive devices have shown a significant effect on upper limb rehabilitation. However, there are many problems, such as bulky and uncomfortable for most of the existing tools. To address the current challenges, we present a soft actuator for structure optimization and size optimization and propose a novel spherical actuator. Also, a prototyped soft wearable exoskeleton is developed. In this paper, the basic principle of the soft actuator is introduced, and the structure and parameter of the actuator are shown in detail. Furthermore, the structure of the actuator is optimized specifically. Besides, experiments are conducted to evaluate the bending property and the output force performance of soft actuators. Lastly, the efficacy of the exoskeleton on the motion of various joints is demonstrated.