Forest transpiration plays an important role in maintaining the water balance of forest ecosystem. Studying transpiration regulations of Quercus acutissima and Quercus variabilis is helpful to understand the hydrology process and water balance of Quercus spp. forest. In this study, the transpirations of Q. acutissima and Q. variabilis were observed continually by the thermal diffusion probe method in Jurong City, Jiangsu Province. Meanwhile, the daily dynamic characters of transpiration and the impact mechanism of climatic factors on transpiration rate under different weather circumstances were studied. The results showed that the daily variation of transpiration rate showed single peak curve in sunny days and cloudy days, and fluctuate peak pattern in rainy days. The peak value was appeared in 11:30—12:30 in sunny days and 13:30—14:00 in cloudy days. The daily mean transpiration for Q. acutissima and Q. variabilis under different weathers were showed as follow:Q. acutissima>Q. variabilis, sunny day>cloudy day>rainy day. The transpiration rate of Q. acutissima and Q. variabilis were significantly positive correlated to the total solar radiation, the atmospheric temperature, and the vapor pressure deficiency. The total solar radiation had the greatest contribution to the transpiration rate of Q. acutissima and Q. variabilis. The contribution rate were 91.7% and 85.5% in sunny days, 71.0% and 80.1%in cloudy days, 50.4% and 57.9% in rainy days. The total solar radiation among climatic factors had the most important influence on the transpiration rate of Q. acutissima and Q. variabilis, followed by vapour pressure deficit, air temperature, and soil water content.