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. 6 m 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 T1. 6 ≤9 ℃ including northeastern China and Qinghai-Xizang Plateau,the warm area with T1. 6≥18 ℃ including the southern China and the middle and lower reaches of the Yangtze River region,the secondary cool area with 9 ℃≤T1. 6 ≤15 ℃ mainly including the northwestern China,and the secondary warm area with 15 ℃≤T1. 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.