Abstract: To improve sealing effects of horizontal gas extraction borehole in current coal seam and solve practical problems of gas extraction for easy-failure boreholes in the sealing segment of soft coal seam with high gas content, the reinforcing dynamic sealing technology was proposed. The basic principle was expounded about the reinforcing dynamic sealing technology, and the Fluent software was used to simulate and analyze the distribution of injection slurry around boreholes by means of numerical simulation, thus the length of different parts of sealing segment had been optimized. The simulation results showed that the optimal sealing length of different parts of sealing segment by the reinforcing dynamic sealing method, in particular, the strengthening section (L₁), the sealing section (L₂) and the strengthening section (L₃) were 6 m, 2 m and 4 m respectively.