Abstract： In the forest ecotone between Betula ermanii forest and Picea-Abies fo rest from 1 525 m to 1 775 m, and the timberline ecotone between B. ermanii forest and alpine tundra from 1 990 m to 2 170 m on north slope of the Chang bai Mountains, using gradient sampling along with elevation, the ecological char acteristics of B. ermanii population were studied, and the survival curve, d istr ibution pattern and competition index of B. ermanii population were analyzed . Fractal structure of B. ermanii population was studied also. The results s howed that B. ermanii population changed from declining type to stable type in B. ermanii Picea-Abies forest ecotone, and from stable type to incr easing type in B. ermanii alpine tundra ecotone according to B. ermanii po pulation survival curve; In the two ecotones, distribution patterns of B. erma nii population were found in disorder, beloning deviated random distribution a nd were at the phase changing area from one type ecosystem to another based on p opulation p attern index; Competition index and box dimension of B. ermanii population i ncreased rapidly in B. ermanii Picea-Abies forest ecotone, and they dec reased quickly in B. ermanii alpine tundra ecotone. Fig 4, Ref 16