Climate change is one of the most serious challenges in the 21st century. Accompanied by the rapid expansion of cities worldwide, the phenomenon of urban heat islands (UHI) has become a critical environmental issue in many large cities. The health consequences of UHI range from thermal discomfort to life-threatening medical conditions. Fortunately, trees and vegetation in the city can be considered as an ecological measure to cool cities. Although there are numerous studies on microclimate-adjusting effects of urban green spaces, the relationship of landscape pattern of urban green space and air temperature reduction is not fully addressed. In this study, by applying field measurement and high-resolution Google Earth Image, we investigated 18 typical green spaces and observed their role in temperature reduction. The results showed that the green space in Shanghai could reduce summer air temperature by 1.17-5.60℃, and approximately two-third green spaces provided a lower cooling effect than the average temperature reduction (2.51℃). The daily temperature reduction of green space was significantly positively correlated with the external ambient air temperature. However, the cooling effect of urban green space was lower when the ambient air temperature was cooler than 26℃. Tree density, leaf area index (LAI), and waterbody proportion inside the green spaces presented the highest influences on the cooling rate. If there is a 5% increase in tree density, 1 increase in LAI or 20% increase in waterbody percentage, the temperature cooling rate of urban green space would be elevated by 1.73%, 1.66%, and 1.18%, respectively. Therefore, we advised the improvement of the cooling effect of urban green spaces in Shanghai through pattern optimization.