Abstract: In this paper, walnut was firstly classified according to variety, and the importance of craching soft-walnut by machine was pointed out. After measuring the physical characteristic of the soft-waluut shell, it was simplified into homogeneous thin shell and its internal force was thus analysed by the thin shell theory. Based on the above, the principle of cracking and extracting kernel was put forward. A machine with doubled serrated-plate and serrated arc was then designed. Experimental test confirmed the optimum parameters of the cracking unit derived theoretically. The performance of the cracking machine; Cracking rate over 90% , high grade kernel rate 70～90% , a-mong which first grade kernel rate 30～40%.