Based on the data obtained from vertical gradient measurements of microclimatic elements of canopy gap in tropical secondary forest of Xishuangbanna in fog-cool and dry-hot season, the daytime characteristics of temporal-spatial distribution and variation of trunk surface temperature, air temperature, water vapor pressure and relative humidity in canopy gap were discussed. The data showed that gap edge had not only a remarkable thermal effect, but also a significant water vapor effect. These effects resulted in environmental heterogeneity in canopy gap. The results provided a basis for further studying heat and water vapor transport, microclimatic formation, biodiversity, and forest succession in canopy gap.