According to the characteristic of gas molecule absorbability in infrared light, remote measurement of vehicles emission CO and CO2 by non-dispersion infrared was investigated in this paper. By using single IR detector, CO,CO2 and background were measured. The combination of gas filter and lock-in-amplifier were used to detect the week signal. Many shortcomings of conventional method were conquered, such as low precision of detection and the detection of vehicles which under real-world driving condition. The relation of gas concentration and signal under immobile condition was also described. The mobile condition results show that the emission from vehicles which under real-world driving condition can be measured online automatically.