Mobile passive differential optical absorption spectroscopy (DOAS) was used for the remote sensing of the emission flux from different systems of a steel factory. Correlation matrix of the absorption cross sections was used for the best DOAS inversion band. Vertical column density was retrieved by this system, combined with the meterorological wind field and car speed information,the emission of SO2 and NO2 in the area was estimated. The results showed that the average value of the flux of SO2 and NO2 was 149 kg/h and 372 kg/h in the rolling and smelting system, 260 kg/h and 286 kg/h in the coking system, 21 kg/h and 26 kg/h in the power system, 64 kg/h and 79 kg/h in the roasting system, and 34 kg/h and 99 kg/h in the sintering system.