HCHO is an important ambient pollutant in urban areas. Ground-based multi axis differential optical absorption spectroscopy(MAX-DOAS) was used for the measurement of tropospheric HCHO’s slant column density in summer 2008 in Beijing. The cross section’s dependence to temperature, I0 effect and Ring effect correction are performed in the spectrum analysis. Tropospheric air mass factor (AMF) is calculated using geometrical approximation method. The tropospheric vertical column density (VCD) is converted from slant column density by AMF, and the variation of HCHO in the experiment period is shown. Compared to GOME-2 and SCIAMACHY’s HCHO results, the correlation is evident.