As the core component of soft robots, the deformation and motion characteristics of soft actuators directly determine the operational performance of the robots. To overcome the high driving pressure and limited structural design flexibility in traditional pneumatic artificial muscles, this study proposes a rectangular bellows actuator. Through finite element simulation comparing the performance of triangular, parabolic, rectangular, and semicircular bellows structures, the results indicate that the rectangular structure achieves the optimal comprehensive evaluation coefficient, combining excellent axial elongation capability with radial stability. Experimental verification shows that under pure pneumatic loading, the actuator can reach a maximum elongation stroke of 53.2% at 60 kPa, with the elongation exhibiting a linear relationship with the number of bellows and a nonlinear relationship with the input pressure. Further simulation analysis reveals that under the coupled action of air pressure and tangential load at the free end, the actuator can effectively suppress bending deformation by adjusting the internal pressure. An equivalent bending stiffness model is subsequently established, indicating that the stiffness decreases with increasing bellows number while exhibiting an approximately linear increase with rising internal pressure. Accordingly, an equivalent bending stiffness model is established, which demonstrates that the equivalent bending stiffness decreases with an increase in the number of bellows and shows an approximately linear increasing trend with the rise in input pressure. In terms of dynamic modeling, a motion equation for the actuator under compressive load at the free end is constructed based on a three-element model, and the model parameters are identified using the recursive least squares method. Experimental results confirm that the proposed accurately predicts the dynamic response of the actuator under different load conditions, with a displacement prediction error of approximately 2 mm. Through the integration of structural design, simulation analysis, and experimental validation, the static and dynamic deformation laws of the rectangular bellows actuator are systematically elucidated, and corresponding equivalent bending stiffness and three-element dynamic models are established, laying a theoretical foundation for its further application in driving and execution fields of soft robotics.