Abstract: The Gushan Formation is a lithostratigraphc unit dominated by shale. According to the new definition, it shows clear diachroneity in the Taihang Mountains. In the south part of Jingxing, the Gushan Formation, 2～5 m thick, is only equivalent to the Blackwelderia Range zone of the lower part of the Gushan Stage. In the Quyang area, it includes the Gushan Stage and the middle and lower parts of the Changshan Stage, placed between the Blackwelderia and Changshania Range zones. In the Laiyuan area it includes the Gushan Stage, the Changshan Stage and the middle part of the Fengshan Stage. It is equal to a biozone between the Blackwelderia Range zone and the Tsinania-Ptychaspis Assemblage zone. So, the Gushan Formation is a lithostratigraphic unit characterized by upward diachroneity and thickening from north to south.