Abstract: In view of the problem that for SDQ fixed-point sampling device, when the coal seam is hard or the ground stress is small, the resistance between hole wall and double wall drill pipe can not stable greater than inner pipe resistance of double wall drill pipe, which leads to poor sampling performance or even sampling failure, this paper proposes solution of adding ring injector to the double channel tail. By means of numerical analysis and field experiment, parameters of ring injector nozzle diameter in double channel tail were studied. The numerical analysis shows that when the inner nozzle diameter is 2.5 mm, the negative pressure of ring injector is the largest, and it is the optimal parameter to reduce the system resistance; the field experiment result shows that when the inner nozzle diameter is 2.5 mm, for the double channel tail of ring ejector, the sampling time shortens, the sampling depth increases and the sampling success rate increases.