The surface thermal condition of Qinghai-Tibetan Plateau is not only important for the local weather and climate, but also for the short-term climate change in the surrounding areas, especially in sub-seasonal to seasonal scale. Soil thermal diffusivity and soil heat flux are two key factors to determine soil thermal condition. The spatial and temporal distribution of soil thermal diffusivity and the soil heat flux in Qinghai-Tibetan Plateau are still not well understood. In this paper, the method of Conduction-Convection was applied to calculate the soil thermal diffusivity and the soil heat flux in Qinghai-Tibetan Plateau by using monthly mean soil temperature at the depths of 0.8 m and 3.2 m in 39 meteorological observatories from 1980 to 2001. Their characteristics of annual and inter-annual variations and the relationship between soil heat flux and plateau monsoon were analyzed and got some meaningful conclusions. The results show that the annual amplitude of soil temperature decreases and phase of soil temperature delays with depth. The soil thermal diffusivity appears an overall decreasing trend from 1980 to 2001. The annual variations of soil heat flux have opposite phase between deep and surface. The annual variations of total heat flux and convective heat flux have the same phase. The monthly mean soil heat flux is negative during the winter, and positive in summer. The correlation coefficient between the soil heat flux and plateau winter monsoon index is -0.53. The soil heat flux is consistent with the plateau summer monsoon index, the correlation coefficient between them is 0.58. Both values pass the T-test with significance of alpha=0.05. These results are valuable for us to understand the plateau air-land interactions.