Abstract: Disclosed are a device of complex gas mixture detection based on optical-path-adjustable spectrum detection and a method therefor, and the device includes: a light source configured for generating an incident beam and emitting the incident beam into an optical gas cell; the optical gas cell, including a cavity configured for accommodating a gas sample, and a reflection module group configured for reflecting the incident beam and a track arranged in the cavity, where the track is consistent with a light path of the light beam in the cavity; a detector module that is connected with the track in a relatively movable manner and is configured for receiving light beams and obtaining spectral data, where an optical path is changed by moving the detector module relative to the track; and a data acquisition unit that is configured for acquiring the spectral data obtained by the detector module.