Abstract: 【Objective】The transpiration characteristics and influencing factors of the dominant tree species Machilus microcarpa in the Maolan Karst forest were determined. This provided scientific basis for further analysis of the hydro-ecological process of the Maolan primary forest and the Karst area of forest protection and ecological restoration. 【Method】 Utilizing the thermal dissipation probe method and a Campbell automatic weather station, the transpiration of the dominant tree species M. microcarpa was continuously monitored from July 2016 to June 2017 in the Maolan Karst forest, and the photosynthetic and transpiration rates of the leaves measured. 【Result】 The diurnal variation of M. microcarpa transpiration rate showed a typical single-peak curve under all types of weather conditions, and displayed a clear fluctuating trend with high transpiration in the daytime and low transpiration at nighttime. Under sunny weather conditions, the diurnal variation trend of the horizontal transpiration rate of a single tree was consistent with that of the photosynthesis rate and transpiration rate at the leaf level. Under different weather conditions, the transpiration rate showed highly significant differences, with the following averages: 122.00 g/h on sunny days, 76.06 g/h on cloudy days, and 19.60 g/h on rainy days. The daily average transpiration rates on sunny days were 1.60, 6.22 times higher than that on cloudy days, rainy days, respectively. The daily average transpiration rates on cloudy days was 3.88 times higher than that on rainy day. The average annual transpiration rate of individual trees in each season went from high to low in summer [(1.86 ± 0.22)kg/d], autumn [(1.71 ± 0.38)kg/d], spring [(1.59 ± 0.13)kg/d] and winter [(1.07 ± 0.39)kg/d]. The individual plant transpiration rate was 570.31 kg, with 82.81% during the growing season(472.29 kg)and 17.19% during the non-growing season(98.02 kg). The highest transpiration rate was in summer(171.65 kg), followed by autumn(155.60 kg), spring(145.04 kg)and winter(98.02 kg), which accounted for 30.10%, 27.28%, 25.43% and 17.19% of the annual evapotranspiration, respectively. Solar radiation and water vapor pressure were positively correlated with the transpiration rate. 【Conclusion】 Solar radiation and water vapor pressure loss were the dominant factors of the transpiration of M. microcarpa, and rainfall was the inhibition factor, whereas wind speed and soil moisture at different depths had different effects on transpiration under different weather and seasons.