Abstract: With the exploration and development of tight oil and gas, mirco pores (pore diameter <30 μm) in reservoir play an increasingly important role in the occurrence and migration of oil and gas. Taking tight sandstone in the ultra-deep (>6 000 m) Cretaceous Bashijiqike Formation in Kuqa foreland thrust belt as an example, laser confocal microscopy, scanning electron microscopy, electron probe, high pressure mercury injection and other sequence parallel characterization experiments were conducted on the casting thin sections by selecting representative experimental samples, so as to analyze the types, characteristics and genesis of reservoir micro pore and its effect on reservoir property. The results show that nanoscale mirco pores are dominantly found in tight sandstone reservoirs of the ultra-deep Cretaceous Bashijiqike Formation in Kuqa foreland thrust belt, including intergranular micro pore, intragranular micro pore and intercrystalline micro pore. Intergranular mirco pores at the micro-nanoscale level are dominant, while intragranular and intercrystalline mirco pores are nanoscale ones. Mirco pores are formed mainly as a result of secondary origin with supplement of primary origin, and corrosion transformation is a key factor for secondary origin. Reservoir microporosity in the study area is about 2.8%, and the contribution rate of mirco pores to reservoir porosity decreases with increasing porosity. Reservoir throat connecting mirco pores is at the nanoscale, with the pore throat radius of 2-400 nm and peak value of 5-50 nm. The pore throat radius with the main contribution to permeability is 20-400 nm. Methane molecules form a viscous flow in mirco pores, making great contribution to gas productivity. Various types of mirco pores are different in scale dimensions, geometrical morphology, intercommunication and gas occurrence and migration characteristics.