根据中国东部33站1884～1995年的四季降水进行了经验正交函数 (EOF) 开展，得到了前三个模态随时间的演变，重点分析与我国北方降水变化有关的趋势及与同期海平面气压距平的关系。夏季降水的第一模态反映在长江和黄河中部与华南沿海的降水位相相反。这一降水模态在20年前的变率较大。当夏季东北亚出现稳定的地面高压距平，中国东部处于气压槽中时长江和黄河中部降水偏多，而当地面高压距平稳定于我国西北和低压距平处于东部海上时降水为负距平。夏季降水的第三模态表现为以长江为界的南北反向变化。秋季降水的第二模态表现为以长江为界的南北反向变化，第三模态表现为东部沿海与西部的反向变化。这些降水模态与一定环流形势相联系，特别是秋季降水的第三模态受台风路径的环流形势所决定。冬季降水的第一模态中心也出现在长江和黄河中部，年代际变化的幅度趋于增强。对春季降水，第一模态表现为长江及其以北的降水与华南的降水反位相。2~3年变化幅度大于年代际变化的幅度。第2模态反映出华北和东北的降水与其它地区的降水位相相反，存在30年左右的位相转换关系。北方地区的春旱从1980年代开始有所加重。

This paper first deals with the empirical orthogonal function (EOF) expansion using four seasonal rainfall data for 1884-1995 in eastern China from 33 stations. The sea level pressure anomalies (SLPA), then, are used to explain the leading modes of rainfall in northern China from the composite of typical years. The first mode of summer rainfall shows the opposite trends in the central area of the Yellow and the Yangtze river basins related to the coastal areas of South China. More rainfall in the area appeared when the positive SLPA occurred in northeast Asia while a pressure trough in eastern China. For the autumn rainfall, the first three modes show a center in the middle and lower reaches of the Yangtze River, reversed trend between southern and northern China, and between eastern coastal and western areas of China, respectively. These modes are closely linked with circulation patterns, particularly for the autumn third mode that was linked to the circulation in the typhoon season. The central area of the first mode for the winter rainfall is located in the middle reaches of the Yellow River and the Yangtze River. For the first mode its amplitude of interdecadal variability gradually became large in the 20th century. The second mode of winter rainfall shows an opposite relation in signs in northern and southern China. The tendency indicates that the decadal rainfall was above normal for the 1920s-1970s but below normal for recent years in northern China. For the spring rainfall the first mode shows a reversed relation in northern China related to South China. The second mode shows that the rainfall in North China and Northeast China was opposite to other regions and a quasi-30-year oscillation is noted in the series of this mode. The dry trend in northern China has become severe since the 1980s.