Abstract: Soft actuators are suitable for gripping fragile and delicate objects with irregular shapes and sizes owing to their high flexibility and have become a current research focus. But current soft actuators have a general problem of insufficient gripping force. To grip objects with different mass and sizes on assembly line safely and reliably, a novel pneumatic soft actuator with jointed endoskeleton structure was developed which separated the actuation and force bearing function. The bending action of the actuator was performed by the soft rubber with embedded radial-restrained fiber through pneumatic actuating, while the gripping force was bore and transferred by means of the jointed endoskeleton. To obtain the pose of free-end of the soft actuator, the theoretical model was built up. Firstly, the strain energy function of silicon rubber (Yeoh model) was used for deducing the stress and strain. Secondly, the relation between bending angle and input pressure was analyzed. Then the pot matrix of the free-end could be acquired through D-H method. Moreover, to determine the size parameters to facilitate the prototype, the sectional radius, the sectional height, the axial length and the wall thickness were chosen as the design parameters to analyze. The influences for bending of the actuator were discussed. The results showed that the input pressure reduced along with the increase of the sectional radius and the axial length while increased with the increase of the sectional height and the wall thickness. Furthermore, an optimization design algorithm was developed based on the theoretical model. At first, the strain-stress curve of the silicon rubber was measured by tensile test and the coefficients of Yeoh model were obtained. The determined pressure and the expected pose of the free-end were defined as the input while the minimum weight was the optimization target. Then 4 key design parameters could be calculated by the algorithm. With the obtained design parameters, the soft actuator was fabricated and relevant experiments were conducted. An experimental platform was developed to test the bending angle of the soft actuator. Through the experiment, the bending angle of the free-end pressurized by each finger-segment only was measured. The variation trend of experimental data was consistent with that of theoretical ones. When the input pressure was below 100 kPa, the theoretical curves coincided with the experimental curves. But when the input pressure was larger than 100 kPa, the theoretical curves were above the experimental curves. The reason was that the silicon rubber presented a high nonlinearity at a large deformation. The maximum difference was less than 9% with maximum working pressure 150 kPa. The modeling error was mainly originated from the friction damping of the endoskeleton joints and the fabrication precision of the soft finger. Therefore, the friction damping term should be considered to improve the theoretical model and a correction coefficient should be added. Another test platform was put up to measure the bending stiffness of the soft actuator. The tip of the actuator could generate maximum output force while it was entirely constrained without bending motion. Then the bending stiffness was defined as the radio of the maximum output force and the bending angle without external force. From the experiment, it indicated that the bending stiffness increases with the increase of the pressure and it could reach up to 4.5 N/rad at the largest working pressure. The bending stiffness was improved significantly and the flexibility was remained. The soft actuator is successful and promising in future development and application.