Abstract: he Late Silurian Xibiehe Formation is a molasse deposition of shallow marine facies in central region of Inner Mongolia.Xibiehe Formation widely unconformites on ophiolitic melange，arc-island volcanic rocks, Caledonian granite and back-arc basin flysch deposition.The unconformabale relationship reveals the complex relationship between the regional structure，which is the evidence of the continental crust accrationary in central Inner Mongolia happened during Caledonian. The Xibiehe Formation has a similar regional tectonics significance to the Old Red Sandstone in the Europe area.