Shell-loosening is of importance in facilitating shrimp peeling. In this study, enzyme and high pressure (HP) improved the shell-loosening at different degrees, which were observed as gaps by microscopy. The shell-loosening gap induced by an endoprotease with broad specificity (Endocut-03L, 53 μm) was much higher than that induced by HP at 100 MPa (HP100, 12 μm), followed by an endoprotease with high specificity (Tail21, 8 μm), and HP at 600 MPa (HP600, 5 μm). The degree of shell-loosening was found to be correlated to the extent of protein changes that were obtained by 2D gel electrophoresis. Shell-loosening due to HP100 and Endocut-03L was mainly caused by physical and enzymatic degradation of high molecular-weight proteins in shell and epidermis and subsequent loss of degradation products, disrupting the structure of muscle-shell connection. However, HP100 was less effective than Endocut-03L due to its stabilizing effect on the shell collagen, lowering its shell-loosening effect.