Abstract: The knoll reef in Lengwu Area composes of sponges and belongs to Lengwu Formation,Maokou Stage of Lower Permian.Up to the present,it is the only one reef discovered in the carbonate strata of Lower Yangtze River Area.The thickness of the crop-out reef is over 60 m with the area less than 1 Km².The reef core lithology is sponge frame-stone and biomicrite.The main frame-building organisms are of sponges and there are diverse attaching organisms.Slip block developed at fore reef while stromatolites developed at back-reef with obviously dolomitization.Both the base and the cap of the reef are attributed to terrigenous elas-tics and most of the facies of strata equivalent to Lengwu Formation in Lower Yangtze River Area changed into terrigenous elastics.The occurrence of the reef is mainly controlled by terrgenous clastics.The various facies belts of the reefs in Lengwu Area are distinct and reflect the possibilities of linear assemblage of the knoll reefs.Therefore,it is hopeful to discover some buried facies reefs in Western Zhejiang.The corresponding locations of the various facies belts for the reefs show the plane configuration of the distribution for land and sea during the period of Early Permian,Maokou stage.It is proved that the Cathaysia did exsit in Maokou Stage and the adjacent seashore line trends northeast.