Abstract: The strong heterogeneity and unclear development mechanism of the Lower Paleozoic buried hill reservoir seriously restrict its exploration effect. In this paper, the characteristics, main controlling factors and distribution rules of the Lower Paleozoic carbonate reservoirs in the slope zone of Nanpu Sag were studied by using core, imaging logging and analytical test data. The results show that the study area develops two types of reservoirs : 'supergene karst' and 'fracture karst'. The reservoir space of 'supergene karst' reservoir is dominated by small dissolution pores, which are concentrated in the high part of the structure and the top of the buried hill within 100 m. The main reservoir space of the 'fracture-dissolved body' reservoir is fractures, with a wide range of distribution, and the reservoir section is generally more than 150 m. Rock type is the material basis of reservoir development, and limestone and dolomitic limestone are the dominant lithology of karst reservoir. Fracture is the core element of reservoir development, and the fracture network system provides a channel for the dissolution of atmospheric water. Paleogeomorphology is the key condition for reservoir development, and the upper slope is a favorable location for karstification. Therefore, the development mechanism of 'lithology-structure-paleogeomorphology' three-element coupling reservoir is established.