Abstract: Experimental study on the longitudinal cracks of 41 corroded reinforcement concrete beams in atmospheric environment is carried out.The concrete cover depth and stress state of the beams have great effect on the longitudinal cracks.It is difficult for the longitudinal cracks to occur with a thick concrete cover.The possibility of the longitudinal cracks occurring at the tensile zone is doubled of that at the compression zone and the possible reasons are also analyzed. The quantitative relationship of longitudinal cracks width and steel corrosion rate is presented, which is valid for estimating the durability of concrete beams.