It is considered that the heat island phenomenon is generated by temperature rise due to heat release from urban structures which have a high heat absorptance and are warmed by solar radiation during the daytime. Applying solar heat high reflectance paint to the exterior surfaces of urban structures would suppress the increase in temperature, and make it possible to mitigate the heat island phenomenon. This paper describes the influence of solar reflectance and transmittance characteristics of top coat with the change of film thickness and the reflectance characteristic of the under coat on the solar reflectance of paint system, while aiming to establish a design method of solar heat high reflectance paint system. The conclusions obtained from this study are as follows : (1) It has a linear relation between log T that is indicated in a logarithm of film thickness T(μm) and solar transmittance τe1 (%). (2) It has been confirmed that the solar reflectance of the paint system is influenced by the solar reflectance of the under coat. (3) It is possible to show the solar reflectance of the paint system as the sum of total solar reflectance (ρe1) of the top coat and solar reflectance (ρe2) which is transmitted by solar radiation considering the reflection on the surface of the under coat.