The water vapor cycle between soil-plant-atmosphere is weakened and its ability for regulation is poor due to the increase in impervious surface areas in urban environments. Therefore, it is of great significance to study the transpiration response of urban trees to environmental factors amidst reasonable water vapor regulation in urban areas. In the growing season of 2017, 58-year-old Pinus tabulaeformis Carr. was selected as a research tree species for sap flow measurement, by thermal diffusion, at the Hohhot arboretum, Inner Mongolia. We measured meteorological factors and soil water content simultaneously and estimated canopy stomatal conductance using the Penman Formula. The results showed that (1) stand transpiration of P. tabulaeformis had obvious daily and monthly changes in the growing season. The diurnal stand transpiration variation graph showed a single peak curve on sunny days. Monthly stand transpiration reached the maximum in May, followed by July, August, June and September, which was 20.96, 19.89, 18.09, 17.25 mm and 7.49 mm, respectively. (2) There were extreme significant correlations between stand transpiration and vapor pressure deficits, global radiation, soil water content, and wind speed (P<0.01). Global radiation, vapor pressure deficit, and soil water content were the main environmental factors affecting forest transpiration (R²=0.47, R²=0.31 and R²=0.16), and wind speed had the smallest impact on forest transpiration (R²=0.12). Different rainfall events had varied effects on stand transpiration, but a significant effect when daily rainfall exceeded 10 mm. (3) In addition to environmental factors, leaf stomata of P. tabulaeformis controlled transpiration in response to environmental factors. Leaf stomata were more sensitive to vapor pressure deficits when it was < 1.5 kPa, whereas, global radiation, when < 250 W/m², promoted transpiration. When the threshold was exceeded, leaf stomata would close to suppress tree transpiration.