To study the physiological mechanisms in environment adaptation of Betula ermanii in treeline of Changbai Mountain, a National Nature Reserve of China, the specific leaf area (SLA), content of Chl(a+b), malondialdehyde (MDA) and the membrane permeability (MP), and the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in leaves of B. ermanii from different altitudes (A1: 1700 m, A2: 1800 m, A3: 1900 m, A4: 2000 m and A5: 2050 m) were investigated. The results showed that SLA decreased conspicuously with increasing altitude, compared with that in A1, it decreased significantly 35.90% in A5; Chl(a+b) reduced with increasing altitude, however Chla/Chlb and Car/Chl increased with elevation; At 1900 m, the content of MDA and MP reached minimum values, as well as the activity of SOD, POD, CAT and APX in B. ermanii leaves, when the altitude near the upper limit of forest vertical distribution, the content of MDA and MP increased and reached maximum values, but the activity of SOD, POD, CAT and APX reduced in some degree. In general, 1900 m is the best for the growth of B. ermanii; while above 2000 m, the physical resistance of B. ermanii declined, which is not conducive to the growth and development. Therefore, a higher elevation may limit its distribution.