The Xiangzhong depression is one of the negative structural unit of Nanhua land-surface sea basin in Late Paleozoic and possess favourable conditions for oil-gas generation. There are 18 gas production well at present, while the overall reservoir properties of the core detection shown as low porosity and permeability, belongs to poor physical property, tight reservoirs. The observation of diagenetic fabric and pores evolution were analyzed based on casting thin sections, SEM, rock grain size, granularity and porosity. The results show that: Porous type, fracture type and porous-fracture type are the main pore types in this area; Secondary denudation pore and tectonic fractures are the main reservoir spaces. Tight reservoirs in Lower Carboniferous were formed since 290 Ma. Diagenesis is impact a lot on reservoir porosity. As compaction is the main factor caused the loss of porosity; Pressure solution, corrosion, fracture change the pore structure effectively on sandstone reservoirs; Later cementation enhanced the tight of reservoirs. Combined with liquid inclusion homogenous temperature research, regional geological background, stratigraphic burial history and the infusing time, we concluded that before the gas accumulated in the trap, the reservoirs compacted. So the precedent deep basin gas is the main potential exploration targets.