The Differential Absorption Spectroscopy (DOAS) is becoming a very important and effective technique of monitoring principal atmospheric compositions such as NO2and SO2, while Multiple Axis Differential Absorption Spectroscopy (MAX-DOAS) is very effective for ground-based measurement.By measuring the scattering solar ultraviolet and visible spectra in zenith and off-axis directions, analyzing the finger spectrum of the trace gases of study, the MAX-DOAS can be used to measure the slant column amount of the trace gases of study by utilizing the DOAS technique.The corresponding vertical column amount can be converted from the slant column amount with an appropriate air mass factor.MAX-DOAS is widely applied in monitoring of air mass quality because of its low price, stable operation, easy maintain, and reliable data products.