Quantum cascade lasers are applied to the remote sensing detection of various types of gases due to their high sensitivity,high output power,and narrow line width.In this paper,a vehicle exhaust remote sensing system based on quantum cascade lasers is designed using wavelength modulation spectroscopy(WMS)technology.The modulated driving signal of the laser is composed of a low frequency saw tooth wave and a high frequency sine wave,which can effectively suppress the background noise and greatly improve the detection sensitivity.The continuous laser with a wavelength of 632.8 nm is used as the beacon light,and the precise angle between the beam combiner and the reflector ensures that the beacon beam is coaxial with the mid infrared laser beams emitted by the four quantum cascade lasers,enabling visual alignment of the light source.After the lasers pass through the exhaust in the open optical path,the light intensity signal is collected by the infrared detector and converted into an electrical signal.After amplification by I/V,the lock in amplifier is used to extract the second harmonic component which is proportional to the concentration of the measured gas.Four exhaust gas components of NO,CH,CO and CO2 are detected simultaneously and mutual interference is avoided.After testing,detection signal of the remote sensing system exhibits extremely correlation with the gas concentration.The absolute value of relative errors of the system dynamic measurement is less than 5% and the detection optical path can reach 16 m,at least to meet the three lane of simultaneous detection.