Abstract: The Mesozoic and Cenozoic in Kuche Depression is predominantly a set of terrestrial detrital formation. In the reservoir sandstones in the area, albite is one of the widely developed authgenic minerals. Micro-structural evidence shows that diagenetic albite occur as euhedral crystals in the pores, and “places feldspar and other detritus along cleavage and micro-cracks. EPMA analysis indicates that same of the alteration product has a chemical composition transitiona1 between the pure albite and the replaced detrital feldspar. For example, composition of replaced alkali feldspar is between microcline and albite, and An content of altered plagioclase decrease continuously. This has been regarded as a direct evidence for fluid replacement, because the feldspar crystallized from solution or magma usually has a fixed chemical composition. On the basis of mineral assemblage observed by SEM , EPMA and XRD , there exist three kinds of albitization: (1)Ab replaces Kf; (2)Ab replaces the assemblage of Kf, Kaol and Q, forming iliite simultaneously; (3)Ab replaces Pl and Q. In reactions(2)and(3), the volume of resultants much less than that of thereactants. And in reaction (1), dissolution of Kf is more apparent than precipitation of Ah, so that the albitization is in favor of development of secondary porosity and improvement of the physical properties of the reservoir. Aagaard et.al.(1990) found that in eodiagenetic zone(2 km)albite makes up 3 to 5％ of the total volume of the rock, while in mesodiagenetic zone(4-5km)it is about 9％ This means that 30～50％ of detrital Kf is replaced by albite. In Kuehe Depression, albite distribution is also correlated to burial depth. XRD analyzing result shows that in the reservoir sandstone below 4000m , the albite content increases with increasing depth, but in the shallower levels, no such relation is found, Taking into account of the distribution tendency of kaolinite. XRD results show that in the reservoir sandstones above the burial depth of 3000 m. 38.9％ samples were found with XRD detectable kaolinite, but in the sandstones below the depth of 4000 m. only 11 5％ samples contain kaolinite. Both of them suffered no surface weathering, with no significant difference in source materials and sedimentation environment. It seems that more kaolinite was consumed in the deeper reservoirs during diagenetic process. It can be concluded that albitization described by reactions (1)to (3)is dependent on geothermal gradient, and mainly takes place in 9O℃～l10℃ thermal girdle. This is in consistent with the view point of Morad et. a1. (1990) and Saigal et a1. (1988)made on the reservoir sandstones in Norwegian North Sea oil field. In North Tarim, most of the proved oil and gas accumulations are concentrated within the burial depth of 4000 to 5500m , corresponding well to the geothermal zone of albitization. At present we can riot say that this means any causal relationship between them , but there is no doubt that albitization contributes a lot for the development of secondary porosity which in turn improves the physical properties of the reservoir.