3ν vibrational absorption band of water vapor lies in the 935 nm spectral region. Differential absorption lidar has much higher measurement sensitivity in this region. Unfortunately, this spectral region is already at the edge of the gain bandwidth of Ti: Sapphire lasers and outside gain bandwidth of Cr: Alexandrite laser. Spontaneous fluorescence radiation of tunable dye laser is higher, which makes their spectral purity declinable. So optical parametric frequency convertor can be used as the transmitter for water-vapor differential absorption lidar(DIAL). The dynamically-stable ring resonator contains dual 70.7° cut, walk-off-compensated KTP nonlinear crystals, which is pumped with an injection seeded, frequency-doubled 532 nm Nd: YAG laser with repetition frequency of 10 Hz pulse. The resonator length of OPO was actively locked by injecting the distributed feedback semiconductor lasers of 935 nm and using "ramp-hold-fire" technique. The average output power of the transmitter was 4.5 W, the pulse length was 6 ns, the conversion efficiency of light (532 nm) to light (935 nm) was more than 17%, and the short-range and long-range frequency stability of light frequency was 30 MHz(RMS). The beam quality M2 was about 7.8, and the spectral purity can reach 99.9%. It will be one of the candidate light sources for remote sensing of atmospheric water vapor profiles.