Abstract: Acidic fracturing fluid can effectively improve the micro pore structure of coal, thereby improving permeability and gas drainage effect. In order to explore the influence law of the acidic fracturing fluid action time on the pore structure transformation effect of coal samples, hydrochloric acid is used to prepare acidic fracturing fluid and immersion tests are carried out with coal samples from Xintian Coal Mine. The results of high-pressure mercury injection and scanning electron microscopy show that acidic fracturing fluid can conduct effectively transformation on the pore structure of coal samples, but the transformation of the pore structure of coal samples is time-dependent. The increase of pore volume reaches 39.1% in the first 8 hours and tends to be stable (45.8%) after 24 hours, mainly due to the saturation of mineral consumption such as calcite, kaolinite and so on; After the action of acidic fracturing fluid, the change of pore composition of coal samples is not significant, still mainly consisting of micropores, transition pores, and macropores; Acidic fracturing fluid will not only increase the original pore size of coal samples but also dissolve minerals and generate new micropores (SEM verification), resulting in an increasing trend in the average pore size and permeability of coal samples. The research results provide reference basis for the application of acidic fracturing fluid.