Abstract: Associated with the continuous implementation of exploration and development of volcanic oil and gas reservoirs, the “inner reservoir” with a large distance below the weathering crust volcanic rocks has been proved to have potential to form large-scale oil and gas reservoirs. However, the study on the characteristics, main controlling factors and distribution law of inner volcanic reservoir is still in the initial stage due to the significantly different reservoir formation mechanism from that of the weathering crust reservoir. By taking the footwall of West Dishuiquan Fault in Dinan Bulge as an example, core samples, thin section, physical properties, logging and seismic data are used to conduct the identification and depth division of inner volcanic reservoir, analyze the lithology, lithofacies and physical properties, and determine the main controlling factors for the development of inner volcanic reservoir. The results show that: (1) The inner reservoir is mainly distributed in the range of 250-600 m below the unconformity surface; (2) The favorable lithofacies (lithology) of the inner reservoir are thermal base wave subfacies (breccia tuff) of explosive facies and the caved subfacies (tuffaceous breccia) of explosive facies; (3) The reservoir space is dominated by dissolution pores, followed by tectonic fissures; (4) The main controlling factors of the favorable reservoir include paleogeomorphology, fault distribution, crater distribution, and volcanic eruption stages. The low-lying trough near the crater is favorable area for the development of inner reservoir. The inner volcanic reservoir is relatively developed near the crater and fault. The vertical distribution of inner reservoir is affected by volcanic cycles, and the inner volcanic rocks overlaid by source rocks are more easily transformed into inner reservoir.