Abstract: This paper discusses the population density of Betula Luminifera with the changes of diameter classes, the dynamic relationship between individual mean weight of Betula Luminifera population and its density. The phasic function was presented of Betula Luminifera population density with the changes of diameter classes. The model between individual mean weight of Betula Luminifera population and the density was also presented. According to the verified data, the model presented in this paper characterizes its higher credibility in the process of natural thinning of Betla Luminifera population. At the same time, it has also a magnificence for the study on self_thinning of the other population.