中文摘要：

利用模糊C均值聚类法对1981-2000年中国157个1.6m地温观测站的20年平均地温值进行了客观分类,将全国1.6m地温场分为四类,并对各类地温场20年区域月距平值进行了集合经验模态分解。结果表明：（1）中国1.6m地温场可以客观地分为四类区域,分别是冷区（T_（1.6）≤9℃）,包括东北地区和青藏高原地区;暖区（T_（1.6）≥18℃）,包括长江中下游地区和华南地区;次冷区（9℃≤T_（1.6）≤15℃）,主要包括西北地区;次暖区（15℃≤T_（1.6）≤18℃）,主要包括淮河流域地区;（2）模糊C均值聚类分析得到的四类地温场的月距平都有明显的准1.5年和准4年变化周期;（3）在1981-2000年间四类地温场的变化趋势分为两种,分别是持续上升型（包括冷区和次冷区）和先降后升型（包括暖区和次暖区）,并且上升的幅度随时间增大,尤其是20世纪90年代以后,四类地温场的增温趋势越来越明显。

英文摘要：

Soil thermal conditions have a significant impact on weather and climate change.The temperature in soil is an indicator of the thermal condition.It represents a change in the underlying heat storage.It is very necessary to do some researches about the soil temperature.In this paper,some characteristics of soil temperature at 1.6m depth of the whole country are discussed.The soil temperature data observed from 157 observatories at 1.6 m depth from 1981 to 2000 has been used.The FCM method was applied to study the similarities and differences of all observatories.As a result,when longitude,latitude and soil temperature of each station are concerned,all observations are classified into four types of clusters.They are thecool area with T_（1.6）≤9℃ including northeastern China and Qinghai-Xizang Plateau,the warm area with T_（1.6）≥18℃ including the southern China and the middle and lower reaches of the Yangtze River region,the secondary cool area with 9 ℃≤T_（1.6）≤15 ℃ mainly including the northwestern China,and the secondary warm area with 15 ℃≤T_（1.6）≤18 ℃ mainly including Huai River basin and its around,respectively.Then,the EEMD（Ensemble Empirical Mode Decomposition） was used to study the quasi-periods and nonlinear trends of the four-type areas.It shows that all areas have similar quasi-periods of 1.5 and 4 years in monthly soil temperature anomaly at 1.6 m depth.The nonlinear trends of the four types of clusters have played in two ways：the constantly warming way（in the cool and secondary cool areas） and the warming after cooling way（in the warm and secondary warm areas）.The warming rate has been amplified with time,especially after 1990,and this warming is something like to be accelerated.