An urban canyon absorbs more sunlight than a flat, open surface due to multiple reflections in the canyon, increasing the urban heat island effect (UHI). One geo-engineering idea to mitigate the UHI to make the conventional pavements more reflective and to return more radiation to the sky. The urban canyon albedo (UCA) are modeled and the model with experimental observations are validated. We investigated whether increasing the pavement albedo can raise the UCA effectively based on evaluating the reflective diffuse radiation from the pavement to adjacent building walls. It is found that the ratio of building's height to the road's width determines the UCA whereas other factors acts secondary roles. During summertime reflective pavements in an urban canyon reflect a sizable additional diffuse radiation to the adjacent walls. Reflective pavements are recommended for only an urban canyon with an aspect ratio no greater than 1.0.