Quantifying the transpiration cooling effect and cooling effect of the shade of different tree species in urban areas is important for improving the vegetation temperature regulating ecosystem services. A small green space patch located in the Qixia District of Nanjing was selected as the study area. The Granier thermal diffusion probe technique was used to monitor the sap flow of three tree species in extremely hot weather. The method "average sap flow of per unit leaf area × leaf area index" was used to estimate the canopy transpiration and transpiration cooling effect. Differences in solar radiation under and above the vegetation canopy were calculated and the cooling effect of the shade of different tree species and the whole green space patch was captured. Finally, we determined the contribution of the transpiration cooling effect and cooling effect of the shade to the total vegetation cooling effect. The results indicated that 1) Diurnal variation of sap flow was regular and was observed to be high in the daytime and low at night. Sap flow typically began at approximately 06:00, peaked at noon, and then showed an obvious midday depression. In the same tree species, sap flow increased with increasing DBH. 2) The volume of the stand canopy transpiration and transpiration cooling effect were found to have the following order: Populus tomentosa Carr > Cedrus deodara > Cinnamomum camphora, and Populus tomentosa Carr (11:00-19:00) clearly peaked later than C. deodara (10:00-15:00) and C. camphora (09:00-16:00). 3) The cooling effect of shade of the three tree species was mostly consistent with the diurnal variation of solar radiation and difference in the average cooling effect between tree species was small. 4) The cooling effect of three tree species and small green space patch was very weak at night and nearly equal to the transpiration cooling effect. The contribution of the cooling effect of shade (60%-75%) to the total cooling effect was significantly higher than that of transpiration cooling effect (25%-40%) during the day.