The study of stand spatial structure is a significant precondition for modern forest management. In 2005, a permanent secondary popular-birch forest plot of 5.2 hm2 was established in Changbai Mountain, in which all trees were measured by diameter at breast height (DBH) and mapped. Its stand spatial structure was studied by means of three indicators, i.e., mingling, neighborhood comparison and neighborhood pattern. The mean mingling and neighborhood pattern of this plot were 0.63, indicating that the forest was above moderate mingling level, and the mingling level of canopy species was higher than that of understory species. The values of neighborhood comparison were from 0 to 0.67, which suggested that all trees were greatly differentiated vertically and the pioneer species of secondary succession were dominant in growth. The value of neighborhood pattern was 0.55, which showed that this forest was aggregated. These characteristics of spatial structure were related to less disturbance, secondary early stage of succession, tree species status in the stand, regeneration mode and reproduction strategy.