CS2, a kind of poisonous gas, with bad smell, is very harmful to people. In China, precise and real-time CS2 monitoring is required in many big cities. With traditional measurement method, it is expensive and time-consuming, moreover it is very difficult to achieve real-time monitoring. A new CS2 measurement method was developed, based on differential optical absorption spectroscopy (DOAS), and the data processing method was discussed in detail. The selection of measurement waveband, steps of data processing and the spectrum dealing with nonlinear method were involved. Also the nonlinear dealing method of standard cross section was realized based on the analysis of lamp spectrum structure in the measuring waveband. With this method, not only the influence of lamp spectrum structure in the CS2 measurement band was effectively avoided, but also high measurement precision was gotten. Three different concentration cells were measured with this method, and high linear relativity was achieved. In the process of real-time and continuous monitoring in some place of Nanjing, a good result was gotten.