Abstract: In this study, the diameter class, growth dynamic, and intraspecific and interspecific competitions of Betula platyphylla were investigated on swamp ecotone. Furthermore, the relationship between competition intensity and diameter class was analyzed. The results showed that there was an obvious sigmoid functional relationship between basal area at breast height and tree height, and the B. platyphylla trees began to shift from height growth to DBH growth when DBH and tree height were 18.3 cm and 19.4 m, respectively. The regeneration seedlings of the B. platyphylla population were rare, and the diameter class of the B. platyphylla population followed a spindle shape. Lognormal function well represented the relationship between diameter and density. The intraspecific and interspecific competition intensity of B. platyphylla accounted for 48.80% and 51.20% of the total competition intensity, respectively. The  intensity of intraspecific and interspecific competition with B. platyphylla followed the order of B. platyphylla (intraspecific) > Larix olgensis > Alnus hirsuta > Populus davidiana > Quercus mongolica > Padus racemosa > Fraxinus mandschurica > Acer mono > Acer ginnala > Ulmus davidiana. The competition intensity of B. platyphylla declined with increasing DBH. However, the competition intensity exhibited little variation when DBH was larger than 20 cm. The relationship between the competition intensity and DBH of target trees followed the power function (CI=AD-B). This model could effectively predict the intraspecific and interspecific competition intensity of B. platyphylla.