Abstract: Hydraulic fracturing is one of the effective ways to improve coal seam permeability coefficient, in order to determine the relationship among fracturing water volume, fracturing time and effective radius of soft and low permeability coal seam. Through numerical simulation and field test, it is found that when the fracturing water volume is a fixed value, the effective radius increases steadily with the increase of fracturing time, the direct proportion relationship between the two is nonlinear; when the fracturing time is fixed, the effective radius increases non-linearly with the increase of fracturing water volume, and the two are positively correlated. The mathematical relationship between fracturing water volume, fracturing time and effective radius is established through regression analysis. The fitting relationship between hydraulic fracturing water volume and effective radius of No.3 coal seam in Xinjing Coal Mine is obtained, the parameters of coal seam water content and gas content in the test area are investigated and verified; when the fracturing water volume is 73.79 m³, the effective radius of hydraulic fracturing is about 51 m, and the fracturing time is relatively optimal.