Through analyses of outcrops, wells and seismic profiles, it is proposed that carbonate slope facies develops in Middle Permian Maokou Formation in northern part of Sichuan Basin. The carbonate slope facies is of typical characteristics as follows: The lithology mainly is dark grey calcirudite, which is composed of bioclastic micrite in majority and sparry bioclastic limestone and reef-building organisms in minor with gravity gliding structure. The secondary lithology is dark grey thin-layered micrite with calcarenaceous turbidite. The evolution of sedimentary facies from Middle Permian Qixia open platform facies to Maokou slope facies reveals a fact of increasing tectonic activity during Maokou sedimentation which resulted in possible differentiation of sedimentary facies belts in northern Sichuan Basin beside other areas. The seismic profile illustrates that the thickness of Maokou strata increases obviously from south to north and is characterized by a sphenoid reflection, which proves the existence of a high-energetic platform-margin facies belt in the south of slope area in the northern part of the basin. This viewpoint is favorable to reconstructing structure-lithofacies paleogeology and predicting the potential sedimentary facies and reservoirs of Maokou Formation in the basin.