Bone is a load-bearing organ in human body. Fatigue damage occurs readily at the modest loads to which bone is subjected during its habitual physiological usage. Even bone fracture may occur during vigorous activity. The nature of fatigue damage is that in bone there are very fine microcracks which are smaller than typical microcracks, and may occur at the level of hydroxyapatite crystals. But bone can repair microdamage by bone remodeling. Osteocytes play an important role of signaling during bone remodeling. Some researchers attempted to describe the process of bone fatigue damage and repair by mathematic, mechanical models in order to understand it well and to apply it well in clinical practice.