Abstract: The Tianyuan Cave site, which was discovered in 2001, is an important paleoanthropological site of late Pleistocene in China. It is located at the Tianyuan Tree Farm, Zhoukoudian Town, Fangshan County, Beijing. The site was investigated and excavated in 2003 and 2004 by a team from the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences. A large number of human fossils (34 pieces) and mammalian fossils (39 species have been identified) were unearthed. The skeleton is dated to be 42 000~38 500 calendrical years by using direct accelerator mass spectrometry radiocarbon, which falls into the MIS 3 (Marine Isotope Stage 3). In order to interpret the possible environmental changes especially the impact on human activities at Tianyuan cave, even in Beijing, the systematic analysis of the mammalian fauna, magnetic susceptibility, clay minerals as well as oxides from sediments was carried out by the authors in the current paper. Sediments of the cave were probably formed by gravitation, and experienced cave development stage, quickly accumulating stage,stable deposition stage and filling stage. The climate may have changed from cold and humid in the forming stage to warm in the quickly accumulating stage, to dry and cold in stable depositing stage, and to warm and humid in the last stage in early Holocene. It should be noted that both the human and mammalian fossils were mainly distributed in layer 3 of breccia, indicating that human occupation in the cave took place in the quickly accumulating stage. In addition, the climate and environment were optimal as a warm temperature with flourishing forest and animals, which may lead to intensified occupation of early human beings. In brief, the studying of human activity environment at Tianyuan cave bears great significance in the research of human occupation environment in Beijing area during MIS 3.