This paper aims to measure a historical impression of streets on the composition of roadside elements. “Grain Theory” was introduced that intends to analyze the character of streets or districts by the density of town element such as shops and housings. The results of an experiment on the historical impression were analyzed by 11 sorts of grains. As a result, some important facts were gained : to get an historical image, over 20-30% of authentic grains were needed, and disturbing grains should be under 10-20% of historical grains. And a formula was shown that predicts the historical impression of a street on the composition of grains. Some measures to reinforce the historical street image were taken from it.