Abstract： The spatial distribution and size of Castanopsis fissa population in subtropical evergreen broad-leaved forest were studied in this paper. Pattern of spatial distribution varied in size classes and scales of observation. The age-class structure of population in young pure forest, among which the age of dominant Castanopsis fissa was 13 a, showed triangle-type, suggesting increasingly growing, and their individuals in all age-classes (divided into seedling, short sapling, tall sapling and adult trees) displayed clumped distribution. The age-class structure of population in middle-age mixed forest, in which Castanopsis fissa also dominated the community and the age of dominant Castanopsis fissa tree was 24 a, showed informal dumbbell-type, suggesting the population had come into declining stage, and their individuals in all age-classes (divided into seedling, short sapling, tall sapling and adult trees) also displayed clumped distribution, but its clumped intensity was stronger than the former. The age-class structure of population in old-age mixed forest, among which the age of dominant trees was 53 a, showed breaking inverse triangle, suggesting the population will disappear with the community succession, and their individuals in all age-classes (divided into seedling, short sapling, tall sapling and adult trees) displayed random distribution. Fig 1, Tab 4, Ref 10