Carbon monoxide, as a kind of dangerous mine gas, can easily accumulate in a complex mine environment poses a serious threat to the safety of miners. This paper presents a compact carbon monoxide detector. This instrument have a mid-infrared quantum cascade laser operating at 465 μm as light source, with mercury cadmium telluride (HgCdTe) detector and 12 m compact absorption path to obtain trace-CO diagnostics. Self-designed high-speed photoelectric signal acquisition system solved the signal chain impedance mismatch problem which caused by commercial oscilloscope. This new acquisition system realized 1 GSPS sampling rate and vertical resolution of 12 bit at 400 MHz sampling bandwidth which improved the detector’s sensitivity and integration effectively. This instrument use long path differential optical absorption spectroscopy (LP-DOAS) theory. The detection limit of the instrument which gives as 108×10-9 is obtained by comparing the residual between the measured spectrum and calculated theoretical spectrum with Voigt broadening. Detector’s measurement error has non-stationary, slowly time-varying characteristics. According to this feature we use Allan deviation to estimated detector’s sensitivity, after about 40 seconds the deviation curve reached the minimum. The Allan deviation value is 61×10-9. In two-hour tests, the stability of the detector is 21×10-3, for up to 12 hours of stability tests, the detector’s stability can still reach 17×10-2. This instrument has high flexibility, through the replacement of different laser with different lasing wavelength; it can be achieved on a variety of trace gas detection.