The present invention relates to the technical field of laser spectrum detection and gas detection, and in particular relates to a two quantum cascade laser spectrum-based multicomponent gas simultaneous detection device and method. An arbitrary waveform function generator outputs a periodic signal which only superposes high-frequency modulation signals in any half period to be used as a laser current signal, a room temperature continuous mode mid-infrared quantum cascade laser is driven by a current control unit, the laser emits a laser signal, the laser signal passes sequentially through a focusing collimating three-dimensional adjustment system, a first mirror, a sample absorption pool and a off-axis parabolic mirror to be reflected to a first detector, the first detector passes the laser signal through a data acquisition unit to convert into an electrical signal and transmit to a computer, and information of the gas to be measured can be obtained by analysis and processing of the electrical signal by the computer. The devices simultaneously utilizes two spectrums for gas detection, and has the advantages of high detection sensitivity, high detection accuracy, no need of external standard gas calibration, simple optical path adjustment, fast response, and stability, and the like.