CO, CO2 and H2S are important components of the atmosphere in the coal-fired boiler. Their concentrations can not only reflect the combustion conditions but also serve as the basis for judging the high-temperature corrosion degree of the water wall. Therefore, it is of great significance to measure the concentrations of CO, CO2, and H2S accurately. In this work, the WM-DAS method and Herriott cell with a length of about 40 m were used to carry out synchronous measurement of three kinds of gas absorptivity under different CO/CO2 concentration ratios at room temperature and low pressure. The results showed that the measured values of the absorptivity of the three gases agree very well with the theoretical calculation values, and the relative error is within 6. 82%, which suggests the highly reliable of this method. Subsequently, the dynamic measurement of CO/CO2 (0~2 000 μL·L-1） and H2S （0~20 μL·L-1) was carried out. The results showed that the measurement system has good linearity in response to the concentration changes of the three components.