Abstract: High diversity and density of lianas is a typical property of tropical rain forest.However,the mechanism of high diversity and density of lianas in tropical rain forest is still under active debate.The dry season hypothesis suggested that lianas exerted higher photosynthesis during dry period than woody species,and thus had the competition advantages with woody species.Nevertheless,none of photosynthesis measurement in the field work was in situ and only the seedlings or the understory leaves was collected. It subsequently reduced the credibility of the data for answer the above mentioned question.Thus,we carried out a field work in a tropical rain forest with strongly seasonal of water during the middle of dry season.Our in situ measurement was inconsistent with previous studies and showed that photosynthesis of woody species was higher than lianas in that period.The further data also showed that woody species can take more carbon for dry matter production than lianas.This study implicated that further ecosystem level field work should be carried out before we confirmed the dry season hypothesis.