Scientific fitness exercises need to master the rules and follow certain principles. According to the scientific basis of human body, kinematics theory and the function and characteristics of exercise on human body, give comprehensive guidance in fitness exercise. Therefore, the principle of survival of the fittest has sufficient scientific basis and can reflect the objective law of the development of things. The principles of fitness mainly include the principle of self-awareness, the principle of comprehensiveness, the principle of gradual progress and the principle of perseverance. It is the experience summarized by people in physical exercise practice, which provides scientific guidance for exercisers to achieve ideal results.