Negative-pressure draw-out type coal layer gas content spot sampling method

The invention discloses a negative-pressure draw-out type coal layer gas content spot sampling method. The spot sampling method comprises the following steps of selecting a proper coal layer testing position, arranging a drilling device for drilling, and arranging a negative-pressure draw-out type sampling device beside the drilling device; in the drilling process, conveying compressed air from the inner part of a drilling rod to the bottom of a hole to blow out drillings from a gap between a hole wall and the drilling rod; when the drilling device drills with a preset sampling depth, stopping the drilling device, and blowing away coal dust retained in the hole through the compressed air; connecting a sampling pipe of the negative pressure draw-out type sampling device with the drilling rod of the drilling device; then continuously drilling the hole, switching on the negative pressure draw-out type sampling device, and enabling fresh coal dust obtained by cutting by a drilling bit to enter a coal sample collector through the drilling bit, an inner pore of the drilling rod and the sampling pipe. According to the negative-pressure draw-out type coal layer gas content spot sampling method, the spot sampling can be realized; furthermore, the sampling time can be shortened; the sampling operation can be finished within seconds; the gas loss of a coal sample is low, and the sampling efficiency is greatly improved; the sampling and the drilling can be implemented synchronously and continuously; the spot sampling method is safe and reliable; the drilling rod does not need to quit.