Based on analysis of drilling cores, thin section, SEM and FMI imaging logging data, it is found that the steep slope belt of the Jiyang Depression hosts abundant secondary porosity, which expands the space of reservoir, and more importantly, changes pore geometry to enlarge porethroat and effectively improve reservoir permeability. The research also indicates that dissolution of acidic components such as feldspar, debris, carbonate and sulfate and tectonic activity are the major factors triggering development of deep secondary porosity. There exist two vertical belts of secondary porosity, with depths ranging from 3450 to 3850 meters and from 4050 to 4575 meters. The main mechanisms are: The main mechanisms are: ①dissolution by acidic fluid derived from thermal evolution of organic matter; ②degypsification, dedolomitization and thermochemical sulfate reduction; ③high pressure accelerates organic matter evolution and offers protection to existing porosities; ④Tectonism, dehydration and contraction, etc.