In order to better detect the vertical profile of the tropospheric atmospheric water vapor, some improvements have been made to the established 935 nm differential absorption lidar. Taking the dual-channel receiving measure, the near-field channel telescope is also a beam expander that emitted laser light. The polarizing beamsplitter and quarter wave plate were used to isolate emitted light and echoed light in near-field channel, cassegrain telescope was applied in the far-field channel(main channel), thereby the near-ground dead zone of the lidar was reduced. The wavelength was shifted to 936.0-936.5 nm. The power of seed laser and the purity of the emission spectrum was increased, thereby the detection accuracy was improved. The detection span range was extended from 600-2 000 m to 250-3 000 m, and the random error was 5%.