Objective: This study aimed to investigate the changes of beef tenderness during dry and wet-aging. Methods: Yanbian cattle was used as material to determine the changes in shear force, pH, moisture content, myofibrillar fragmentation index, protein degradation and histological properties of muscle fibers within 30 days after dry and wet-aging. Results: With the extension of aging time, the shear force of dry and wet aging beef samples decreased significantly, and the shear force decreased from 91.7 N to 51.6 N and 39.8 N at 30 days of aging, respectively. The myofibrillar fragmentation index and myofibrillar protein degradation changed significantly. After 30 days of wet aged beef samples, the muscle membrane was degraded， and the muscle fibers were tightly arranged. The high molecular weight myoplasmic proteins such as creatine kinase and aldolase in beef were decomposed into small molecular proteins, and their concentrations increased with increasing variety. Conclusion: Postmortem aging significantly improved the tenderness of beef. The fragmentation of myofibrillar fibers, the degradation of myoplasmic protein and the connective tissue in muscle cells of wet aging samples were stronger than that of dry aging samples, which had a greater impact on the tenderness of the meat.