A differential absorption lidar (DIAL) system at 935 nm is built for water vapor detection. Its transmitter is based on seed injection ring optical parametric oscillator (OPO), and a narrow linewidth pulse laser is used as pump source. The resonant cavity of OPO is locked by Ramp-Hold-Fire method, and the OPO can generate narrow linewidth and stable wavelength pulse laser with pulse power of 45 mJ, wavelength of 935 nm, repetition frequency of 10 Hz and pulse duration of 6 ns. To obtain water vapor concentration profile of convective boundary layer in Shanghai, the foundation vertical differential detection test is carried out. The detection wavelength is 935.776 nm and the reference wavelength is 935.860 nm. The receiver mainly includes a telescope of 305 mm diameter and an avalanche photo diode sensor. The range resolution is 30 m and the temporal resolution is 60 s. Signals in a range from 600 m to the top of troposphere boundary layer in the daytime and in the nighttime are effective, with water vapor concentration error not exceeding 0.1 g/m3. When we compare the DIAL data with the radiosonde data nearby the meteorological station, the availability of the DIAL data is confirmed.