Abstract:Thinning is one of the important methods of forest management and human disturbance to forest ecosystem. Researching on different thinning methods, intensity and frequency has an important significance for rebuilding and recovering the intrinsic function of forest ecosystem and achieving sustainable forest management. 31 Platycladus orientalis plantation stand plots were used for researching the arbor and under-vegetation growth variation and diversity. Results showed that different thinning intensity increasing the diameter, height, crown and stand volume growth. The amount of the growth indices after different thinning intensity related to the site type. Heavy thinning intensity could been fit for the high quantity site and the low or middle intensity fit for the low and middle quantity site. The amount of undergrowth vegetation species has an increasing trend after thinning with low and medium intension but decreasing after the heavy intension. The Simpson index and the Shannon-Wiener index became larger after thinning, and the value increasing throw time. The Shannon-Wiener index was more sensitive with the thinning intension. Biomass of the under-vegetation was increasing with the thinning intension and the time. Interspecific competition of Platycladus orientalis plantation ecosystem has a close relationship with site type. The better site could endured the heavily human disturbance and the growth balance would been easily broken by the disturbance in a worse site.