The understanding of mechanical performances and microscopic failure mechanisms of cortical bones under service condition is necessary prerequisite of fracture prevention, which would support the development of bone tissue engineering and design of bionic bones. By using miniaturized horizontal in situ compression tester, the effects of both temperature and sampling orientations on the compressive strengths and fracture morphologies were investigated. The significant difference between fracture strengths and compressive strains at various temperatures indicated that the cortical bone was sensitive to temperature. Direct experimental evidences revealed the gradually fibrotic trend of fracture surfaces as a function of sampling orientation. Through the Haversian canals distribution analysis, the relationship between the distribution of Haversian canals and fracture path was established. Essentially, the competition between high density Haversian canals and stress concentration factor determines the initiation and propagation of cracks.