A flexible threefinger manipulator was designed by using a selfmade variable chamber pneumatic actuator. The deformation and stiffness of the flexible gripper were improved by changing the structure of the actuator chamber in turn. The deformation model of variable chamber pneumatic soft actuator was established, and the relationship between cavity bulging deformation and the air pressure in chamber was analyzed. Simulation analysis and static experiment were carried out to obtain the deformation characteristics and the positive pressure of different contacts under different air pressure. The results show that the threefingered manipulator has good flexibility and compliance, and the actuator with variable chamber structure can improve the deformation and clamping force of the soft gripper.