Abstract: This paper focuses on temperature-lowering and humidity raising effects of open and green areas with regard correlation between ecological effects and structural characteristics of green areas in Taiyuan City. Ten green areas from two different categories were selected as samples. Meteorological data along horizontal and vertical belts of the green areas were synchronously examined by HOBO Pro Temperature/Humidity External Logger. The results show that temperaturelowering and humidityraising effects are significantly positively correlated with area and green quantity index, but negatively correlated with P/A （perimeter / area ) index of open and green areas along horizontal belts. The results also imply that temperature-lowering and humidity-raising effects are significantly positively correlated with green quantity; LAI has a significant impact on temperature-lowering effect, but less impact on humidity-raising effect. Ecological effects of urban green areas are largely dependent on green quantity. This highlights the importance of evaluating green quantity in urban green areas. It emphasizes the importance of increased proportion of large area green patches and green quantity as a means of enlarging green zones. Moreover, it is feasible to adopt green area shapes with different P/A values according to their functions, which effectively improves the benefits of urban green areas.