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Shell cracking to extract the kernel is a crucial step in the advanced processing of walnuts. Addressing the low shelling efficiency and inadequate kernel integrity associated with current cracking methods, the finite discrete element method (FDEM) was employed to simulate the fracture process of walnuts under extrusion-shear loads. A extrusion-shear cracking technique was proposed. Initially, physical parameters such as shell thickness and shell-kernel gaps of the Wen 185 walnuts were measured to construct and calibrate the simulation model. Subsequently, both qualitative and quantitative analyses were conducted to examine how the shelling angle under extrusion-shear loads affected the fracture of the shell and kernel. The relationship between shelling angle, compression amount, and the fragmentation of the walnut shell and kernel was also investigated. This clarified the cracking mechanism under extrusion-shear loads and the reasons for kernel damage. The results showed that the cracking mechanism of walnut shells and kernels involved the following: the walnut shell fractured primarily under tensile stress, generating penetrating cracks on the contact surface, which facilitated rapid shell-breaking. In contrast, the walnut kernel fractured predominantly under shear stress. During the shell breaking process, the walnut kernel tended to come into contact with the shell at multiple points, leading to stress concentration, which caused kernel fractures and hindered the preservation of kernel integrity. As the compression increased at different cracking angles, the continuous force exerted on the walnut shell caused inward movement, progressively increasing the damage to the walnut kernel. Based on these mechanisms, it was suggested that after the initial shell fracture, the application of cracking force should cease to allow for deformation recovery time. Subsequently, applying intermittent loading forces can reduce multiple contact points between the shell and kernel, enabling multiple shell fractures with minimal displacement and effectively reducing kernel damage. Finally, a co-directional roller cracking method was proposed to achieve multiple small-displacement shelling, which was validated through experiments. The preliminary optimization results showed that with roller speeds of 33 r/min and 28 r/min and a shelling gap of 33 mm, the shelling rate reached 96.9%, and the kernel integrity rate was 84.3%. Compared with traditional counter-rotating shelling methods, the shelling and kernel integrity rates were improved by 7.7 percentage points and 3.2 percentage points, respectively. The research result can provide a theoretical reference for enhancing walnut shelling efficiency and kernel integrity.