To reveal the mechanism of injection increase and deepen the understanding of the initiation and propagation mechanism of fractures in fracturing flooding，we studied the influencing factors of breakdown pressure with the physical simulation test of fracturing-flooding. The experimental results show that the breakdown pressure of rock samples rises with the increase in the injection rate，decreases exponentially with the increase in rock permeability，and grows linearly with the rise in confining pressure. On the basis of micro-CT scans，the characteristics of fracture distribution in fracturingflooding were analyzed on a micron scale.The results show that in the process of fracturing-flooding，vertical fractures are formed along the radial direction and distributed in a plane，and on a micron scale，the fracture propagation path winds along the grain boundary.Combined with the physical simulation test of fracturing-flooding and the micro-CT scans，the porosity，pore diameter，and fracture aperture were introduced as pore structure parameters，and a method suitable for physical simulation of fracturing-flooding and quantitative characterization of fractures on a micron scale in low-permeability reservoirs was established. This method can accurately characterize the breakdown pressure of fracturing-flooding and the width and morphological characteristics of fractures on a micron scale.