Abstract: Breaking walnut shell is the preliminary stage of processing walnut. Irregular shape of walnut shell and small clearance between shell and kernel are found by practical measurement. Experiments proved that the distortion value needed in the safe outburst of walnut shell is bigger than the clearance. Much broken kernel must be produced by generally mechanical extrusion to thresh shell. The finite element method of structure-static analysis is used in this study. The stress distribution and strain of walnut shell under different conditions of force were analyzed by establishing the geometric model and the finite element model for threshing walnut shell. The optimum forcing pattern of producing smaller distortion and more local crackles easily extending was found. A guiding mechanism has been designed. Experimental researches show that the guiding mechanism lets axis of roller for threshing walnut shell and the long axis of walnut ellipse parallel. It is advantageous for extending crackles, walnut shell is entirely cracked, the kernel-obtaining ratio is higher, broken kernel ratio is less, and the quantities of producing kernel in accordance with excellent character are more.