The characteristics and genesis of grain shoal carbonate reservoirs were studied by using the data of drilling, log-ging and core in Lei 3 member of Middle Triassic Leikoupo formation in Sichuan Basin. The results show that the residual in-tergranular preservation reservoirs and syngenetic karst reservoirs are the main genetic types of grain shoal carbonate reser- voirs. Residual intergranular pores and intergranular dissolved pores are main reservoir space of residual intergranular preser-vation reservoirs, and tubular throats and neck throats are developed. Relatively good configuration of the pore throat leads to the characteristics of medium porosity and medium permeability and good capacity. The isolate intragranular corroded pores and mould pores are main reservoir space of syngenetic karst reservoirs, and throat is less developed. Configuration of medi- um pore and micro-throat leads to the characteristics of medium pore and low permeability. The grain carbonate developed in the marginal platform and interior platform provides the early material basis for the two types of grain shoal reservoirs. The thickness of a single shoal body directly controls the reservoir and permeation form of the two types of grain shoal reservoirs. Diagenetic evolution plays a key role in finalizing the shape of the two types of grain shoal reservoirs.