Abstract: It is widely reported that green roof can lower building surface temperature and cut building energy consumption. However, few studies have explored the annual energy effects of typical green-roof types in hot-summer-and-cold-winter areas. Taking Nanjing as an example, this research investigated the annual energy performance of three green roofs, extensive, semi-intensive and intensive, using the building energy simulation software EnergyPlus. Based on the simulation results, a cost-benefit analysis was performed for the three green roofs. The results suggest that green roofs can regulate roof surface temperature through the evapotranspiration and thermal insulation processes, which are characterized by a cooling effect in summer and a dominant warming effect in winter. The summer cooling intensity can reach 29.3℃, and the maximum winter warming intensity is 13℃. The reduction/increase of roof surface temperature in summer and winter respectively lead to the decrease of building cooling/heating loads. The summer cooling load of the extensive, semi-intensive and intensive green roofs can be reduced by -0.4%, 2% and 2.4%, respectively. The winter heating load of the three green roofs can be reduced by 16.5%, 23.1% and 28.3%, respectively. As a result, the annual energy-saving rates are 1.9%, 4.9% and 5.9% for the three green roofs, with the top floors accounting for 11.1%-71% of the total savings. The cost-benefit analysis reveals that the intensive green roof has the highest net present value and the shortest payback period, but none of the three green roofs can recover the investment cost through the energy-saving benefits during their 40-year life cycle. The above findings may contribute to roof-greening and low-carbon practices for cities in similar climate zones as Nanjing.