An observational field plot, covering an area of 60×60m, was established to analyze the spatial distributions and associations of the main tree species in a spruce-fir coniferous and broadleaved mixed forest in the Changbai Mountain area in northeastern China. The spatial coordinates, diameters at breast height (DBH), diameters at ground height (DGH) and heights (H) of all trees with a height exceeding 30 cm and a dbh less than 5 cm were measured. The univariate O-ring function was used to analyze the spatial distribution patterns of the main tree species while the bivariate O-ring function statistic was used to analyze intraspecific and interspecific relationships among different trees. The distribution of tree diameters at breast height (DBH) of the entire community and of individual tree species follows the shape of an inverse J, which is rather unexpected because the distribution of dbh's in these forests is usually bimodal. All the Abies nephrolepis and Acer mono trees show an aggregated spatial distribution at short distances and a random distribution at other scales while Picea koraiensis、Pinus koraiensis and Tilia amurensis are randomly distributed at all scales. At different growth stages, the main tree species have different spatial distributions. Seedlings and saplings of Abies nephrolepis and Acer mono are spatially aggregated at close ranges but show uniform or random distributions at large scales. Spatial associations between the seedlings, saplings and big trees were also studied. As expected, the intensity of the spatial aggregation is declining with increasing dbh's. With few exceptions, pairs of the five main tree species, show mostly positive association at short distances.