Abstract: In view of the current technological parameter and effects of nitrogen injection fire prevention in goaf, the influence factor of nitrogen diffusion radius is rarely considered, and the theory of nitrogen diffusion radius is lack of corresponding research and application. Based on the measured data of spontaneous combustion hazard area in goaf of Wudong Coal Mine, the influence of nitrogen flow rate on nitrogen diffusion radius was analyzed. Using OriginLab data analysis software to analyze the mathematical relationship between nitrogen injection flow rate and nitrogen diffusion radius, and the calculation of the nitrogen diffusion radius of the nitrogen injection flow rate from 700 m³/h to 1 200 m³/h, carried out to clarify the effect of nitrogen injection flow rate on the nitrogen diffusion radius. The results show that as the nitrogen injection flow rate increases, the distribution range and width of the oxidation zone in goaf decrease, and the nitrogen diffusion radius increases in a nearly linear logarithmic form. With the change of nitrogen injection flow, the technological parameters of nitrogen injection should be adjusted in time according to the nitrogen diffusion radius, so as to achieve the best effect of nitrogen injection.