Abstract: The principle and system design of DOAS indicated the system could monitor multi-gas from UV wavelength to IR wavelength. After a series of test and identification from TüV, the DOAS system had proven to have a good performance on continuous emission monitoring in stationary pollution source and waste incineration, especially to monitor Hg, HCl, NH₃ and HF. The DOAS system could monitor different concentrations of process gas with several paths using one analyzer and work well where was corrosive, high temperature and high level dust,which made it possible to monitor progress gases. The system also could monitor different concentrations of gases in different places. No extract sample system, faster response speed, multi-component and multi-path monitoring by one analyzer laid foundation for the DOAS a good competition on the market.