The climate changes taking after the project of transferring water from south to north are studied. After the project is executed, the river's water level will be lowered, the water velocity will be slowed, the water surface will be narrowed in the middle-and-down reaches of Hanjiang river. The middle-and-down reaches of Hanjiang river are distributed into 11 zones by cities, the changes in water surface evaporation caused by the narrowness of water width are studied and the model of relationship between temperature, humidity and evaporation are established. The average temperature and humidity in every zone in 2000 are used as the initial temperature and humidity, which is taken into model to calculate, so as to achieve the change of temperature and humidity in every zone under different water transferring scale.