Abstract: With the measurement of physiological parameters and semilethal low temperature of 3 different ages of Phyllostachys edulis under natural overwintering condition, the coldresistant ability and its mechanism were studied. The results indicated that, with the decrease in air temperature under natural lowtemperature conditions, the chlorophyll content of 1 year,2 year and adult Ph. edulis decreased first, increased then, and decreased at last by a margin of 21.46 %，42.38 % and 22.76 %， respectively. The variation of SOD activity was similar with that of MDA content, which increased first and decreased at last, POD activity increased first, decreased then and increased at last, the content of soluble protein of 1 year, 2 year and adult Ph. edulis increased first, decreased at last by a margin of 16.43 %, 29.46 % and 29.61 %, respectively. The content of soluble sugar in adult Ph. edulis was higher than that in 1 year and 2 year Ph. edulis. Semilethal low temperature was the lowest (-18.393 ℃) in adult Ph. edulis, second (-15.426 ℃) in 2 year Ph. edulis and third in 1 year Ph. edulis, which indicated that the coldresistant of Ph. edulis was strong and increased along with the increment of age. LT50 was significant positively correlated with the content of soluble sugar in late January, but negatively correlated with the content of MDA in early December.