Based on the radiosonde data in Gansu Province, an analysis of the climate character of the vapor content and the vapor flux in the air, and the vapor source or transportation condition is made. As the result, the vapor content and the vapor transportation in the air are more in quantity in summer but less in winter, more in south and less in north. It is the increasing periods from February to July and the decreasing period from August to January. The cradle of transporting vapor mainly contains the Bengal bay, the South China Sea and the East China Sea, the Qingzang Plateau, and Sichuan Basin. The route of transporting vapor mainly includes middle-level southwest path, southerly middle-low-level path and southeast path.