Abstract: The water metabolism and balance during the period of trees' hibernation were studied. The results show that at the beginning of the period of trees' hibernation , the water content of experimental trees is between 39.36% and 49.86% (Nov.30) ；to Mar.10 of the next year, it drops to 34.05%～41.03%; then it rises up till the middle of March. During this period, the optimum water content is about 35%～50%. But trees are easily hurt by cold condition while water content is beyond 55%，yet trees are very difficult to reproduce while water content is under 25%, and even they would die when water content is under 20%. Within 100 days (from Nov.30 to Mar. 10) of trees' hibernation, the average value of trees' water metabolism changes from -53.1kg to -88.3kg. Trees can utilize 139.5～211.4kg water, and consume 192.6～299.7kg water to sustain trees' water metabolis m negative balance.