The Three-River Headwaters Region (TRHR) in China is a critical ecological barrier as well as soil and water conservation area. In order to analyze soil erosion status variation and find possible causes,the intra-annual distribution and inter-annual variability of sediment load were investigated based upon actual observation data from 1956-2010,by using Mann-Kendall test and other statistical approaches. Meanwhile,we tried to find the possible causes of soil erosion status change by using meteorological,remote sensing,soil sampling data and the double mass curve,Revised Universal Soil Loss Equation (RUSLE). The results showed that: (1) The sediment load in the Yellow River Basin (YRB) was larger compared with that in the Yangtze River Basin (YARB) and the Lancang River Basin (LRB). The continuous three months' maximum sediment load appeared in June,July and August,while the minimum monthly value usually appeared in December and January. (2) The fluctuation of sediment load was relatively violent; the highest decadal value appeared in the 1980s. Over the period of 2005-2010,sediment load in YRB was - 32.25% lower than mean value; however, for YARB and LRB, it was 24.76% and 41.86% higher than mean value, respectively. Soil erosion amounts in YRB increased obviously; however,the change of soil erosion amount in YARB did not show a consistent trend. The soil erosion intensity in LRB decreased to some extent. (3) The causes of soil erosion status change include two aspects of climate change and ecological engineering. On the one hand,increased rainfall led to increase of rainfall erosivity and water discharge,so that soil erosion amount and sediment load increased. On the other hand,after the implementation of ecological projects,the soil organic matter content increased,but it was still lower than the level in 1980. Vegetation coverage increased over the period 2000-2010; however,the root layer did not recover significantly,which played an important role in the soil retention function,so the soil retention function basically did not improve. The research showed that soil erosion status variation in TRHR was jointly influenced by rainfall change and ecological engineering,and the ecological consequence of ecological engineering still had local and temporary characteristics. The arduous task of ecological construction should not be ignored.