Based on analysis of the Lower Permain Maokou outcrops and drilling cores in the northwest of Sichuan Basin, it is shown that the main reservoir belongs to Maokou Member 3 and exhibits the low porosity (average 0.895,) and low permeability (average 1.696×10-3μm2). The reservoir rocks consist of dolostone, bioclastic limestone and crystal limestone. Reservoir space, which includes intercrystal pores, intercrystal solution pores, intragranular and intergranular solution pores and cracks, is divided into pores (less than 2mm in diameter), holes (greater than or equal to 2mm in diameter) and cracks. Solution pores are the common reservoir space and cracks are the important infiltration channels in Maokou reservoir. Diagenesis and sedimentary facies control the reservoir development, in which high-energy biological beach facies in platform is the most favourable to reservoir development and dolomitization and dissolution are the constructive diagenesis.