Abstract: With the aid of analytical results of core samples,thin sections,scanning electron microscopy analysis, porosity and permeability,the present paper gives a detailed description of the reservoir characteristics and diagenesis of the Jialingjiang Formation in the Huaguoshan region,southern Sichuan Basin. The boundaries between the top and bottom of the Jialingjiang Formation are well defined,and the first and second members of the Jialingjiang Formation occur as the main reservoir rocks. Lithologically,the reservoir rock types principally consist of muddy dolosiltite,sparry calcrudite and calcisiltite. The pore types comprise intercrystal pores (solution openings) and intragranular solution openings. The reservoir spaces types contain the porosity type and fissureporosity type. The hydrocarbon reservoirs are dominated by the Ⅲ-type reservoirs with low porosity and low permeability. The diagenesis may be separated into constructive diagenesis,destructive diagenesis and retentive diagenesis. The meteoric water serves as the basis of the formation and development of the hydrocarbon reservoirs in the penecontemporaneous and supergene stages. The dolomitization and burial dissolution play an important constructive part in the formation and development of pores and fissures. The structural fractures may provide the channels for the migration of dissolved fluids. The restoration of diagenetic evolution and porosity evolution is based on the diagenetic sequences,and the dissection,accompanying,accompaniment (association) and replacement of the secondary minerals.