Abstract: The direction of the muscle fibers(parallel or perpendicular to the direction of the muscle fibers)affected edible quality aspects of the beef. From muscle fibers and connective tissue these two aspects,the causes of the differences were explored. The shear force,connective tissue mechanical strength,texture,collagen cross-linking were measured and the structure was observed by scanning electron miuroscope(SEM),by heating bovine semitendinosus for 30,60,90,120,150 min at 60,70,80,90,100 ℃ water bath. The key factors affecting the tenderness of the muscle fiber direction were obtained by the correlation analysis. The results showed that the shear force,hardness and cohesiveness of the connective tissue were significantly higher than those of the parallel direction(p<0.05). Shear force in the direction of vertical muscle fibers was significantly positively correlated with the mechanical strength and chewiness of the connective tissue(p<0.01),significantly positively correlated with hardness,adhesiveness and hydroxylysyl pyridinoline(p<0.05);and the shear force in the direction of parallel muscle fibers was extremely positive correlated with hardness,cohesiveness,adhesiveness,chewiness and resilience(p<0.01),and a negative correlation with the mechanical strength of connective tissue(p<0.05).The vertical direction of the tenderness characteristics of muscle were determined by fibers and connective tissue,the parallel direction of the tenderness characteristics were determined by a small number of connective tissue and muscle fiber extrusion force.