Abstract: Oil and gas exploration has confirmed that the deep low to ultra-low permeability sandstone reservoirs in the central anticline of the X Sag in the East China Sea contain abundant natural gas resources. However, the geological understanding of oil and gas resources in low-permeability to ultra-low permeability reservoirs is not yet deep, which greatly restricted the increases of oil and gas reserves and production in the East China Sea. The Y Structure is the largest inversion anticline structure in the X Sag. Through in-depth analysis on the characteristics of source rocks, reservoir properties, and diagenesis, combined with its thermal burial history, we elucidated the evolution process of low to ultra-low permeability sandstones in the main production layer of the gas reservoir, and clarified the impact factors on the low to ultra-low permeability and the coupling relationship between reservoir diagenesis and reservoir formation. Results show that during the reversal period of the Longjing Movement, the amount of the thickness eroded from the Huagang Formation in the Y Structure exceeded 1 200 m, indicating that the sandstone reservoir of the Huagang Formation experienced the maximum burial depth in history and the highest temperature in 13 Ma, making it easy to form low to ultra-low permeability sandstone reservoirs. According to the degree of densification and evolutionary characteristics of sandstone reservoirs in the research area, three sets of the gas reservoirs were recognized: the H3 sand layer of the Huagang Formation composed of low-permeability gas reservoirs, the H4-H5 reservoir formed while forming ultra-low permeability gas reservoirs, and the H8-H12 reservoir formed first and then ultra-low permeability gas reservoirs. On this basis, combined with the analysis of the process of oil and gas reservoir formation, a reservoir formation model of “two-stage vertical filling in Huagang Formation and adjustment-migration in Longjing Formation” was established in the central anticline belt.