Abstract: In the process of freeform surface machining, the clamping force will deform the workpiece, and then affect the machining accuracy of the workpiece when the conventional metal structure is used to clamp the workpiece. Therefore, three other free optical surface clamping methods are presented in this paper. First of all, the theoretical calculation was completed when the metal structure clamping method was used, and the deformation of the workpiece caused by the clamping force was obtained. Then, a low melting point alloy was used as the clamping material of the clamping program, the experiment and results completed and evaluated. And then, the method of adding the workbench was designed to realize the clamping of the workpiece, the freeform surface processing experiment of the clamping program was completed, and the testing and evaluation were carried out. Then, The freeform surface machining experiment of the fused silica glass material was completed, and the workpiece was tested and evaluated. The experimental results show that it is feasible to use low melting point alloy as filling material for thin-walled partsmachining clamping, and the material removal rate is only 1/2 of the conventional method, and the machining accuracy is also significantly improved. In addition, the machining accuracy of different surfaces processed by the two clamping methods is 0.006 mm and 0.005 mm respectively, which fully meets the machining accuracy requirements of corresponding free-form surfaces.