Green roof has been recognized as a complement of urban green and an ecological solution to mitigate urban heat island (UHI) effects. The benefits of green roof in microclimate at the building scale have been identified by previous studies, but some quantitative data of the wider influence on neighborhood microclimate are still needed. Therefore, a field measurement was conducted in Chongqing to investigate the green-roof effects on outdoor microclimate. From the derived data, it has been verified that the thermal benefits of green roof begin from the high temperature noon to the next sunrise, and the humidification effect was more prominent at night, the most significant cooling effect of plants was at the surface. Meanwhile, the leaf area index of plants was inversely correlated with the amount of reflected radiation. The Sedum Makinoi had the best combined effect of three plants, the maximum cooling temperature was 11.7℃ during the day and the temperature was 4.64℃ and 3.97℃ respectively at 300 mm and 700 mm, the maximum humidification effect appeared at 19:00 at sunset and humidified 33.1%.