Abstract: To improve the depth of gas extraction borehole in soft coal seam, the drilling technology of flushing fluid is proposed. According to the characteristics of coal seam gas extraction borehole, the powder-based flushing fluid and liquid-based flushing fluid were prepared, which passes through the impact test of drilling tool performance and field application test. The results show that the solution can improve the output torque and speed of the motor at the bottom of the hole; with the function of automatic degradation, the hole will not block the gas extraction channel, will not affect the gas extraction; it can significantly improve the viscosity of the flushing medium, so as to effectively improve the slag discharge capacity of the flushing medium, and help to improve the depth of gas extraction borehole in the soft coal seam.