A technics method of automatically changing bottom bobbin case of industrial sewing machine was proposed, along with the design of corresponding changer that realized the method. The structure of the chuck device was analyzed, which was a major component of the grasping changer. Through simulation analysis, the appropriate input pressure range of the chuck device cylinder was determined. Finally, a sample of the chuck device was made, and an experiment relating to the chuck device grasping the bobbin case was implemented. The experimental result shows that the principle of the grasping chuck device is correct and the structure is reasonable. But a few improvements must be made to the contacting faces between the chuck device and the bobbin case, so as to increase the reliability of grasping and positioning.