Abstract: The closed form of pre-crack specimens is an important factor affecting their failure mode and breaking mechanism. In order to systematically explore the influence of the form of crack closure on the fracture mechanism of fracture specimens, four kinds of pre-cracked specimens with different opening widths are made of concrete by inserting thin slices, then the uniaxial compression tests are carried out using the RMT-150B tester after the curing process. The results show that the variation of the peak strength of pre-cracked specimens with different dip angles is consistent with the theory of sliding crack model when the friction coefficient (μ) of crack surfaces is zero and the opening width is 0.1 mm except 0.2, 0.4 and 0.8 mm. In order to explore the breaking mechanism of the specimens with an opened crack under compression, the contribution of normal and transverse compressive stresses to the stress concentration on the crack faces is analyzed based on the superposition principle and progressive field of stress in the region of the elliptic hole, and the formula for the circumferential concentrated stress of an elliptical crack with an arbitrary inclination angle is proposed. In addition, the development characteristics of micro-cracks and the breaking mechanism of pre-cracked specimens during the failure process are also analyzed and discussed. Finally, based on the theory of linear elastic fracture mechanics, the mechanism of shear stress on the development of microcracks at the pre-cracked tip is discussed.