As the typical arid and semi-arid rocky mountain, the mountain area in Beijing has a barren soil and little soil water resource ,which has been the most important limit factor to the survival rates of trees and forest growth in this area. Platycladus orientalis are the principal tree species in this area and theyplay a very important role in water and soil conservation, water-reserving, etc. So it is extraordinary vital for us to study soil moisture,physical features and nutrients condition. The characteristics of soil in the main forest land in Beijing area has been studied in this research by the ways of establishing plots and chronic position monitor so as to make the best advantage from the limited natural precipitation, increase the soil water resource, and make the trees best utilize it by forestry measures. Additionally, the paper may afford scientific thereunder in increasing the survival rates of trees and forest land productivity, expanding forest resources, restoring plant, making the best use of the function of water-reserving on the premise of adaptable tree for adaptable stand in the arid and semiarid areas.