Abstract: Based on 60 different aged dominant tree data in Larix olgensis Herry. plantations， saturated density model was built， and then complied the reasonable density table by diameter series. According to the table， we chose 26 plots which had similar values with reasonable densities of different age stages as test samples. Investigation and statistical results of mean values of diameter increment， diameter distribution and volume in the 26 plots were used to analyze and access the process and effect of thinning. Results showed that stand density declines with the increment of diameter， and an exponential functions of N=3 847345 1e-0082D was available for estimating reasonable density. The reasonable density table showed the optimum densities of age series between 06-08 cover closure. Average stand density before thinning of 26 sampling plot was 2 883 trees/hm2， and average stand densities after 3 times thinning were respectively 2 000， 1 400， and 1 000 trees/hm2. In mature forest， the density was 600 trees/hm2， crown competition factor （CCF） was 41633， the whole volume was 24212 m3／hm2， and the ratio of bigdiameter log was 5926 ％.