The purpose of this study was to analyze the form of composition and principle of reduction in architectural composition. Theorical category is to find reduction system with the connection between idea of society and tradition in compositional frame. The results were as follows : First, it is appeared the mimesis of style. The mimesis of style is differentiated characteristics between Greek Style or Roman Style and Gothic Revival or Renaissance Revival. Second, it is the reduction of primitive of form. It si divided with mimesis of nature and reduction of primitive hut. Like Laugier the former find the architectural prototype, the latter is convinced of simplicity, purity of nature with us.