[Objective] The aim was to study on biological characteristics of photosynthetic response for young trees of B. macrostachya in seasonal rain forest, providing scientific reference for protection of tropical rain forest under change of global climate. [Method] Young trees of B. macrostachya in Xishuangbanna tropical forest were chosen to research in foggy season, dry and hot season, and rainy season to measure dynamics of season changes. [Result] For young trees of B. macrostachya in Yunnan Province, Pn max was the biggest in rainy season, followed by dry and hot season and foggy season at 4.08, 2.89 and 1.81 μmol/（m·s） respectively; Gs and Tr in rainy season were the highest and WUE in dry season was the highest; Gi achieved peak in foggy season, of which the highest values were 0.18 and 1.59 mmol/（m 2 ·s）, and 7.35 μmol/mmol and 455 mmol/（m 2 ·s）; Ci showed an opposite trend with that of WUE, and Gs and Tr changed similarly. [Conclusion] Young trees of B. macrostachya in seasonal rain forest are of significant seasonal change in photosynthetic response, and young trees are shade tolerant.
