Relationships of the vegetation and active layer are the foci of global change study since the interaction between the vegetation and hydrothermal processes of the active layer are important part of Qinghai-Tibet Plateau permafrost ecosystems, and they are liable to react on the global warming and anthropogenic activities.Based on the analysis of soil temperature and unfrozen water content of the active layer,surveys of vegetation,the influences of vegetation on the variations of hydrothermal processes of the active layer in the source area of the Yellow River(SAYR)are studied.Preliminary results show that variations of unfrozen water content and soil temperature of the active layer are significantly affected by vegetation cover,aboveground biomass,and dominant species.The distribution unfrozen water content is consistent with the vegetation coverage.The offsets between the ground surface temperature and air temperature,which are affected by the vegetation cover,are higher in winter-time and lower in summer-time.The beginning of freezing is latter,the finishing of freezing is earlier,and the duration of freezing is longer for those sites with higher vegetation cover.With lowering of vegetation cover,zones with higher content of unfrozen water shift towards the bottom of the active layer.This study reveals the effects of variations of vegetation on soil temperature and unfrozen water content of the active layer for warm,and high-altitude permafrost in the SAYR,and will also facilitate the research and protection of cold eco-environments in the SAYR.