Containing abundant spectral information, wide spectrum laser can simultaneously detect many gases. This paper simulates the simultaneous detection of multiple poison gases by using wide spectrum laser lidar and maximum likelihood estimate methodology. The simulation results show that, the wide spectrum laser lidar in far-infrared wave band can effectively detect the three gases of Sarin, Tabun, VX simultaneously within the range of one kilometer, and the average error can be controlled within 5%. In addition, the detection result differs from the different far-infrared wave bands, it is necessary to choose the wave band combining the spectrum absorption characteristics of the gases to make the measurement error as small as possible. Comparing of three far-infrared wave bands, 9~10 μm 10~11 μm and 10~11.5 μm, the paper analyzes the detection errors of Sarin, Tabun, VX ,and gets a conclusion that 9~10 μm band is the best.