Abstract: Hydrostatic High Pressure(HHP) is a new and advanced technology applied in meat industry. Changes of sensory characteristic, microscopic structure of myofibrils, activities of crude Calpains and shear force value of mutton skeletal muscle under the condition of HHP treatment were studied. The tenderization mechanism that HHP improved the tenderness of mutton skeletal muscle was systematically discussed. Sensory evaluation results showed that muscle color faded and mortem flavor emerged when pressure increased to 400 MPa. Sarcomere contracted, Z-lines broke, M-lines degraded and I band whitened as mutton skeletal muscle was treated with HHP of 400 MPa and pressure keeping time of 10 min. The activity of crude Calpains(P＜0.01) and shear force value (P＜0.05) decreased significantly with the pressure increasing from 100MPa to 400 MPa. At the level of 400 MPa, the activity of crude Calpains almost inactivated. As a result of these findings, HHP treatment the ageing and tenderness of mutton skeletal muscle could be improved by HHP treatment.