The working principle of an internal gripping device of the manipulator based on worm and worm gear and crank connecting rod drive is introduced. Its mechanical properties and calculation formula are also given out. After the device being driven by gear motor,output torque rotates the worm first and transmits the driving force to the worm. Then the worm rotates the upper and the lower worm gears which are meshed with it separately and the worm gears sway the upper and the lower crank connecting rods articulated in worm gears.Lastly,two times amplification of the force by the force-amplifier of the upper and the lower crank connecting rods is realized. The gripper can stick close to the object or the inside surface of workpiece accurately,then grip the object and hold it tightly in balance. The device has the characteristic of compact structure,easy operation,time-saving and less effort,well flexibility and high greenization.