A device for collecting exhalation gas and aiding measurement of a trace component in the exhalation gas and the usage method thereof are disclosed. The device comprises an alveolar air bag for storing alveolar air collected from the breath of a subject, a cavity channel air bag for storing cavity channel air from the subject, a three-way pipe, and a mouthpiece. The three-way pipe comprises a first branch pipe, second branch pipe, and third branch pipe communicating with each other. The first branch pipe and the second branch pipe respectively extend in opposing directions along the same axis. The third branch pipe extends along a radial direction of the first branch pipe and the second branch pipe. The mouthpiece communicates with the first branch pipe. An air hole of the cavity channel air bag communicates with the second branch pipe.
