In this paper, we focus on composite shadows between skyscrapers and other buildings and quantitatively evaluate the multiple effects on the sunshine environment of city-blocks. We consider not only the increase of the shadow time but also the additional superpositions of shadow to analyze sunshine environments in detail. Since these two factors have complementary relationships, so they enable us to divide the effects of composite shadow. Main results of this paper are as follows: (i) the superposition of shadows have a stronger impact to congested building area than the increase of shadow time does; (ii) the effect of shadow superpositions is almost as same as that of shadow-increasing in throughout the day.