Precipitable water vapor (PWV) is one of important green-house gases in the atmosphere. It affects on the energy balance of the land---atmosphere system. The evolution of cloud and precipitation has a strong relationship with the PWV. In the climate change, PWV has a positive effect on the temperature. Ground-Based microwave radiometer can all-time non-attentioned measure the PWV. Three PWV different measurements are compared. The PWV mean bias between the radiometer and the radiosonde is 0.281 cm. The PWV mean bias between the radiometer and the GPS is 0.322 cm. The PWV mean bias between the GPS and the radiosonde is 0.728 cm.

In Beijing, there exist different diurnal variations in different seasons. The mean diurnal variation is about 0.162 cm in Autumn, 0.130 cm in Winter, 0.229 cm in Spring, and 0.276 cm in Summer. Moreover, the maximum PWV appears mostly at 0 AM or 11 PM during the four seasons. The minimum PWV is same with the maximum PWV, except that the minimum PWV appears at 10 AM in Winter.

The variation PWV per hour decreases in the order of Summer, Autumn, Spring and Winter. Moreover, in every season, the percentage of the positive variation PWV per hour and the negative are nearly 50%.

The hourly relationships between the PWV and the temperature are analyzed for the four seasons. The same hourly coefficients decreased in the order of Autumn, Spring, Winter and Summer. In Autumn, Spring and Winter, the hourly coefficients are all positive. However, in Summer, the hourly coefficients are negative from 9 o'clock to 22o'clock.