This study focused on the structure and the platform of the road space of historic districts. We analyzed the road networks of 16 historic districts in Japan from the perspectives of circularity, accessibility and indirection based on graph theory. By calculating and comparing the indexes of each road network (NW1 and NW2) forms, we quantitatively describe the effects of the main prefectural roads (more than 4 m in width) and narrow streets (less than 4 m in width) on the spatial characteristics. And it turned out that we could divided the 16 objective historic districts into 4 types. Moreover, we qualitatively studied the characteristics of each type of historic districts based on their development background and the structure of road network.