Abstract: The displacement mode of the improved extended finite element method can reflect the true crack tip displacement and the stress intensity factor can be obtained without post-processing, so it is convenient to analyse the crack propagation process. In order to study the laws of crack propagation process, the reinforced concrete three-point bending beams having different steel reinforcement ratios and different positions are simulated by using the improved extended finite element method.The basic theory of the improved extended finite element method is studied, the governing equation is derived by using the virtual work principle, and then the stress intensity factor calculation method is described. The crack propagation process of the reinforced concrete three-point bending beams with different parameters is simulated by using the improved extended finite element method. The research results show that the initial fracture toughness is independent of reinforced ratio for surplus reinforcement beam. The fracture toughness reaches the minimum values when the bars are in the critical positions, which are larger when the bars don’t run throughout the cracks than the bars running throughout the cracks. The bolt should be placed in the front of crack tip when the structure containing macroscopic crack is reinforced.