Many movements start with the lower limbs, which motivate the torso to the upper limbs. One of the most significant current discussions in sports is how athletes may decrease their sport injuries. The incorrect movement and the wrong application of force will result in sport injuries easily. In order to jump higher and run more quickly, athletes should rely on tough leg strength. Therefore, the strength of legs plays the important role in any sport. Recently, along with the science and the technological progress, the sport competitions become more intense than past. It is necessary to evaluate the leg strength of the athletes with scientific equipments. Discover the problems and try hard to improve them;Athletes could have a better performance and gain better results. This essay will focus on the data which was measured by Biodex system 4 to discuss the maximum leg strength and the relation of sport performance. Moreover, the balance of the hamstring strength, the risk factors of injury, and the prevention are also discussed in this article.