Through comparison of internal surface temperature (IST) of green roofs with that without green roofs through field measurement and statistics analysis, green roof under natural convention climate in summer was analyzed. Distribution frequency and sum of IST under the conditions with and without green roofs were investigated by dividing IST into several ranges. It is shown that the frequency of IST lower than 34 ℃ for green roofs was 90%, which was about 1.6 times of that for roofs without green. While the frequency of IST exceeding 34 ℃ for green roofs was 4.6% of that for roofs without green, and the sum of IST exceeding 30 ℃ was about 1/3 of that for roofs without greening. Moreover, the property of thermal insulation of green roofs had strong positive relation with outdoor temperature. The thermal insulation characteristic was better as outdoor temperature grew up.