The active oxygen content, MDA content and electrolyte leakage in the leaves of Betula platyphylla seedlings increased under the soil drought stress. Activity of cell defense enzymes changed markedly when the stress of draught was intensified. SOD activity increased then decreased, POD activity decreased and CAT activity decreased then increased. All above physiological index returned to approach the normal level before stress after the water of soil was recovered. The active oxygen content, MDA content and electrolyte leakage in the leaves of Betula platyphylla seedlings increased under the soil drought stress. Activity of cell defense enzymes changed markedly when the stress of draft was wasified. SOD activity increased subsequently decreased, POD activity decreased and CAT activity decreased then increased. All above physiological index returned to approach the normal level before stress after the water of soil was recovered.