When performing grasping tasks, current mechanical grippers often cause damage to the surface of objects, especially objects with very soft surfaces. In order to improve this dilemma, this paper proposes a design of a composite mechanical gripper based on thermoelectric materials. The solution is to replace the original end effector with a thermoelectric material. The thermoelectric material is made into a cylinder, and an expansion material is adhered to its inner surface so that it expands after heating, thereby achieving the grasping of the target object. This innovative design can effectively reduce the risk of damage to the surface of objects caused by traditional mechanical grippers. This paper will also introduce in detail the design concept and grasping principle of the composite mechanical gripper. The experimental results show that the gripper can flexibly control the force of grasping objects at different temperatures, making the composite gripper safer. This design concept can provide new ideas for the future intelligent development of industrial robot fingers.