Abstract: According to cast liquid photo,scan electron microscope,impressing hydrargyrum,quality etc.,the research thinks that clay minerals membrane of the lower Donghetang reservoir of the Devonian in well qun 6 area of the Tarim Basin is divided into original cause and self-generating cause,among them with self-generating cause for most.Clay minerals membrane usually comes into being in earlier diagenetic stage(or developing together diagenetic stage),which have a just relation to the face porosity of the reservoir,and a negative relation to the pore structure.Porosity of the lower Donghetang reservoir developing clay minerals membrane is most of 7%~17.6%(mean of 11.53%)and permeability is most of(0.1~10)×10^-3μm²(mean of 4.15×10^-3μm²),and these quality is obviously higher than the upper Donghetang reservoir not developing clay minerals membrane,whose mean porosity is 5.23% and mean permeability is 2.88×10^-3μm².Clay minerals membrane has a close relation to depositional facies,temperature and pressure system of reservoir,earlier hydrocarbon infusion.Generally speaking,clay minerals membrane develops in lower-middle shore face more familiar,while is short in the upper shore face and foreshore where clay is washed cleanlily.Hydrocarbon infusion in earlier diagenetic stage and abnormal high pressure system(well qun 6 area pressure coefficients for 1.59)have crucial function to protect clay minerals membrane.