Abstract: The West Sichuan Basin has become an important area of natural gas. In the evolution of the foreland basin, 8km thick clastic rock was deposited. Under the double effects of sedimentation and diagenesis, normal and anomalous two types of natural gas reservoirs can be formed frow shallow to deep strata. They can be further divided into 6+1 ranks. The major pay bed is low-permeable ultra-dense sandstone. Its permeability and pore throat texture are very sensitive to the net pressure of overlying strata. Based on the analysis of confining pressure permeability and mercury-injection data, the technical and economical gradation of reservoir quality mainly marked by in situ (formation) permeability K_ms is set up correlated to the well-testing data, and the difficulties and technical strategies for the exploration and development of dense and ultra-dense sandstone gas pools are discussed.