Abstract: E. pleiospermum,an endangered tree species endemic in East Asia,is mainly scattered in the riparian zone in Xiaozhaizigou Nature Reserve. In order to discover the causes of its concentrated distribution and maintaining mechanism in this area,by adopting the method of quadrat method,from the size of the population structure,static life table,survival curve,and space distribution pattern data,studies were made of its quantitative characteristic and spatial distribution pattern. The results showed that:1) both its individual number in the young-age period was few,relatively many in the mid-age period,and also very rare in the old age period. This spindle-like structure displayed that the size of its population belonged to the recession type; 2) Existing grade Ⅰ and Ⅱ had very few individual number,thus the individual mortatity in the static life table of the level Ⅰ and Ⅱ was negative,the individual mortality peak appeared in the grade Ⅳ,and reached the highest level in the grade Ⅶ; 3) Although the seedling survival rate was low,but its sapling survival rate was higher,therefore the survival curve was close to Deevey type Ⅰ. This indicated that E. pleiospermun easily survived in this area; 4) The spatial distribution pattern of its population was an aggregation distribution and its trend was consistent with the most rare plant species. Some population protection measures were recommended,such as moderately disturbing community,appropriately enlarging the gap size. These measures would promote its seed germination,normal development of its seedlings and saplings,and the individual's natural diffusion as well.