The time-space structures of long-term trends and the decadal-scale variations of seasonal temperature and precipitation over China and Mongolia are investigated by using the 5-year moving averaged data from 1951 to 1990. An empirical orthogonal function (EOF) technique is applied to seasonal temperature and precipitation. The changes of atmospheric circulation patterns with these trends, and long-term fluctuations are deduced by using 500 hPa height and surface pressure fields. The correspondence of these components with the Northern Hemispheric surface air temperature (NHT) is examined. The increasing linear trend in the annual mean temperature is remarkable, especially in the northern part of China and Mongolia, while the decreasing trend is conspicuous in the area from Sichuan to Yunnan Province. The increasing trend in the annual mean temperature is due mostly to the anomalies in winter and spring. These trends in winter temperature are directly related to the decadal-scale change of the locations of Siberian High and mid-tropospheric trough over Eurasia, and are associated with the hemispheric circulation changes. The annual precipitation, in contrast, does not show a clear linear trend over the whole of China except in the southern part of China, where a significant increasing trend is noted. Summer precipitation shows a remarkable decadal-scale fluctuation in the first two dominant EOF modes. The first EOF represents the increasing trend in the middle and northwest part of China, while the second EOF represents the oscillation between the southern part of China and the rest of the country, which is closely related to the summertime NHT.