Abstract: In the land-atmosphere interaction, land surface conditions such as soil thermal condition ( soil temperature, soil thermal conductivity etc.) and soil moisture etc., have significant impact on atmospheric circulation and climate change. The Loess Plateau is the second biggest plateau in China with a vast territory, which lies athwart semiarid, arid and semiwet area. The land-atmosphere interaction on the complex underlying surface not only directly affect climate and environment changes of the Loess Plateau, but may also have an impact on those of East Asia, or even global. The study regarding soil heat condition and soil temperature of the Loess Plateau region is one of the most important components in the land-atmosphere interaction research on the Loess Plateau. The data used in this paper were quoted from the observed data at Pingliang thunder and hail test station by Chinese Academy of Sciences, cold and Arid Regions Environmental and Engineering Research Institute, as well as the soil temperature data from Baimiao plateau Central Meteorological Tower from October 2005 to November 2006. The field observation data during three consecutive years from 2004 to 2006 in Pingliang Baimiao Plateau on the“ Loess Plateau of land-atmosphere interaction observation experiment study of (Loess Plateau land surface” process field EXperiments, LOPEX ) in 2005 have also been analyzed. In this paper, we analyzed on soil temperature conditions of different underlying surfaces, as well as the causes of the diversity in underlying surface temperature distribution and variation from soil physical angle. The results have been shown as below: over the near surface layer, the soil temperature amplitude decreases gradually with the increase of soil depth, but do not change significantly at the depth lower than 40cm. As the seasons change, the soil temperature has two steady states during the whole year. The first one appears in early April, with the value of around 6 ℃; the second one appears in midNovember and the value is 14 ℃. For the soil temperature of the whole year, there are a low center (the value is below zero) from December to next February and a warm center from July to August. All of the layers have the lowest temperature on January, and then rise up during the rest of whole year. During April and May, the soil temperature has a rapid increase and reach the maximum in early August. After this soil warming period the temperature begins to decline. The soil temperature gradient has a significant daily variation. The soil heat is transmitted from the deep to the surface at night. With the sun elevation angle increased, the soil temperature gradient become negative and the deep soil obtains energy from the surface.At about 19∶[KG-2mm]00 in the evening, the temperature gradient turns to be positive. The amplitude of soil temperature gradient covered by vegetation is significantly smaller than that with no vegetation coverage. The daily average thermal conductivity are 1.43，1.24，1.17 W·m^-1·k^-1 over Chaisi, Yuanxia and Zhongxin station, respectively. The difference of soil physical properties and soil texture is the one reason that there is variability among each station in the soil temperature and soil heat conductivity.

Key words: Loess Plateau, soil temperature, thermal conductivity