Abstract: The Chinese arborvitae, as an important species of silvicultural tree, is a kind of evergreen coniferous tree widely distributed in the northern part of China. It can even grow in the crevices of limestone due to its ability to endure poor soil and dry habitat. Natural secondary forests or cultivated trees are widely distributed on sunny and half-sunny slopes of mountains in the district of Beijing at elevations of 200–900m. The floristic composition of natural Chinese Arborvitae forest is mainly consisted of various species of Compositae, Graminae, Leguminosae, Liliaceae and Rosaceae. Especially, species of Compositae and Gramineae are abundance.The plant life form spectrum of Chinese arborvitae forest shows that Hemicryptophytes and Phanerophytes are rich, they make up 38% and 37% of total species, respectively. Geophytes occupy 12% of total species, Therophytes and Chamaephytes are 8% and 5%, respeetively. According to significant corelation between diameter at breast height, height of tree and the dry weight of stem, leaves and roots, the optimum models are obtained by the dry weight of various tree parts (W) against diameter at breast height of tree: W(stem) =l69.82D1.92 (P<0.001),W(branch)=28.64D2.41 (P<0.01), W(leaves)=10D2.82(P<0.001), W(roots)=e4.99+0.387D(P<0.001).The biomass of stem, branches, leaves and roots in Chinese arborvitae plantation are 15.56 t/ha., 6.57 t/ha., 5.16 t/ha. and 5.29 t/ha., respectively. The total biomass of tree layer is 32.58 t/ha. The biomass of shrub and herb layers shows seasonal change, they are 7.17 t/ha. In September. The total biomass of Chinese arborvitae plantation are 39.75 t/ha.