Cool roofs are the roofs that can deliver high solar reflectance and high thermal emittance. The benefits associated with cool roofs include reduced cooling energy load, reduced air pollution and greenhouse gas emission, and improved human health and comfort. This study attempts to develop standard measurement method for evaluating the reflectance and emmittance of a cool roof material. First, a literature survey was conducted to analysis the current programs promoting the use of cool roofs in the world, and then more than 2000 cool roof materials¡¦ data were collected in this study. In addition, the dynamic building energy load simulation by using eQuest was conducted to investigate the energy-saving benefits of cool roof applied in Taiwan. The results indicated that the reflectance, emmittance and thermal conductivity have a significant effect on the roof heat gain. The higher reflectance or emmittance of the roof, the less heat gain absorbed in the roof. But, reflectance has a larger effect on roof energy-saving than emittance does. The energy-saving effect by using cool roof on the flat-type roof is larger than on low-slope type roof.