Some concrete samples taken from Shiziya tunnel in Hubei province were analyzed by XRD, SEM/EDS, BSEM/EDS, optical microscope and micro hardness device. It is shown that deterioration of concrete in the form of cracking, and decrease of cohesion and strength are caused by the internal sulfate attack caused by gypsum bearing dolomite coarse aggregates. Ettringite and thaumasite are formed in the interface transition zone between gypsum in the coarse aggregate and mortars. Therefore, the structures of the interface transition zone and the matrix are loose and porous, the micro hardness is reduced.