In this paper a new technique of differential absorption lidar (DIAL) was presented for environmental SO2 measurements. The fourth harmonic of Nd:YAG laser was used to pump CH4 and D2 gas cell, and their first Stokes Raman-shifted wavelengths of 288.38 nm and 289.04 nm were gotten. Laser beam of 289.04 nm is rather strongly absorbed by SO2, but another laser beam of 288.38 nm is weakly absorbed. This wavelength pair of 288.38 nm and 289.04 nm can be used to measure environmental SO2 concentrations. Based on this technique, a SO2 DIAL was constructed. SO2 actual measurements and primary studies were also carried out at lidar located site. Measurement errors were analyzed and evaluated. SO2 concentrations measured by SO2 DIAL are comparable with results obtained by SO2 analyzer.