Based on the soil temperature data obtained in IOP period of GAME-Tibet, 1998, the monthly changes of daily variation features of the soil temperature in D110 site, the northern part of the Xizang Plateau, have been analyzed. The results show that the soil temperature existed evident daily variation in summer season (May-September). It is a sine curve and consistent with solar radiation. However, the phase lagged as the depth increase. In winter season (October-April), there was also daily variation, but the amplitude was relatively small. As to the study period, the maximum daily variation appeared in August 1997. Then it decreased. In May 1998, the daily variation increased suddenly and reached to the highest point in June 1998. Meanwhile, the variation of the minimum temperature was small and gentle, but the maximum was large. In summer, the daily variation of the soil temperature at 40 cm depth is also evident. Its variation is fundamentally a sine curve and consistent with solar radiation. However, its phase is lagged as the depth increase. The transport direction of energy between surface and its below layer could change two times in summer. In winter, although the soil temperature showed relatively evident daily variation and played as sine curve, the temperature on surface was always below that of under layer. Even the surface could absorb the solar energy, but it was too little. The energy was transported from lower layer to upper layer all the day in winter.