Due to extremely effective advantages of the quantum cascade laser spectroscopy and technology for trace gas detection, this paper presents spectroscopy scanning, the characteristics of temperature tuning, system resolution, sensitivity, and system stability with the application of the presented gas sensor. Experimental results showed that the sensor resolution was ≤0.01cm–1 (equivalent to 0.06 nm), and the sensor sensitivity was at the level of 194 ppb with the application of H2CO measurement.