Abstract: This paper deals with the structure and dynamics of Platycladus orientalis population at the forest area in loess plateau of northern Shaanxi Province. The results are as follows: 1. Platycladus orientalis is a pioneer species of the forest succession in this rigion. But the population at rocky steep slopes or ridges may develop into stationary community.2. The size structures are classified into seven types: initial growing;growing-stational;stational;declining;extremely declining;residual and disclimax types.3. The population density tends to decrease with the population and succession development,and ,has significant negative correlation with coverage of arbor layer,age of Platycladus orientalis population and moisture of soil.