Abstract: During the field implementation of hydraulic fracturing of coal seam, there are some problems such as complexity of coal seam destruction and blindness of construction. Analysis of the flow law of hydraulic fracturing fluid in coal seam can not only optimize the hydraulic fracturing construction parameters, but also provide a basis for the layout of coal seam extraction drilling after hydraulic fracturing. Therefore, the radial flow model of fluid during hydraulic fracturing was proposed. Guided by this model, the field test of hydraulic fracturing was carried out in 1307 working face of Guojiahe Coal Mine. The results show that under a certain water injection pressure, with the extension of fracturing time, the water area radius and permeability coefficient of fractured coal seam further increase. At the same time, the concentration and purity of gas extraction in this coal seam have been greatly improved after hydraulic fracturing, within the influence radius of hydraulic fracturing, the further the extraction hole is from the pressure fracture hole, the greater the increase of gas extraction purity and concentration. The field test proves that the theory of water and gas replacing has good applicability in the application of hydraulic fracturing of coal seam.