Abstract: After twice research climax of 1890-1910 and 1950-1970, once more research on planation becomes a hot topic again, and it will come to the third climax. This paper, based on morphologic and tectonic analysis, and provenance studies, confirms that the gently sloping surface on the top of Songshan Mountain is a planation surface formed during the late Eocene. The surface also correlates with the similar ones from North China and other continents around the word.