Abstract: Research on population pattern distribution is one of the most active research fields in plant population ecology.It was showed by the preliminary study on the population distribution patterns of Pinus tabulaeformis and Platycladus orientalis plantations in the mountainous area of Beijing that the population distribution of the young plantations for both tree species was in even distribution pattern, but the pattern varied in different site conditions and at different development stages.Along with the increment of age and diameter class, the distribution pattern of Pinus tabulaeformis plantation shifted from even distribution to random distribution, while the distribution pattern of Platycladus orientalis plantation on sunny slope with thick soil changed from even distribution to random distribution, but for the Platycladus orientalis plantation on sunny slope with thin soil the pattern would change from even distribution to clumped distribution.The study results will be helpful to determining the thinning method for the young plantations in the mountainous lithosol area with varying site conditions(with site heterogeneity) in north China.Distribution pattern features such as clumped distribution should be referred prior to taking the spatial evenness into consideration while selecting remaining stems in plantations.