The utility model discloses a negative-pressure gas detecting sampling auxiliary device, which belongs to the technical field of pipeline gas detecting equipment and is used for detecting negative-pressure gas in a pipeline. According to the technical scheme, the negative-pressure gas detecting sampling auxiliary device is composed of an inserted sampling pipe, a locking nut and an air pump, wherein an inner hole of the locking nut is arranged on the wall of the inserted sampling pipe in a sleeved manner; the air pump is installed on the rear part of the inserted sampling pipe; the rear part of the air pump is provided with an air pump outlet connected with a bleeder through a hose; the wall of the bleeder is provided with a bleeder sampling pipe; the inner hole of the locking nut is internally provided with a pressing flange and a seal ring. The inserted sampling pipe provided by the utility model is inserted into a negative-pressure coal gas pipeline; negative-pressure gas is pressurized by the air pump, and then is exhausted from the bleeder; the bleeder sampling pipe on the bleeder is opened, and a handheld CO or O2 analyzer is directly close to the bleeder sampling pipe; the pressurized gas directly blows a detection head of the handheld CO or O2 analyzer for detection. The negative-pressure gas detecting sampling auxiliary device provided by the utility model is simple in structure and convenient to use, and eliminates the potential safety hazard caused by the fact that qualification judgment is only based on experience without data in the process of purging a negative-pressure coal gas pipeline.