Abstract: Based on the tests of 20 simply support reinforced concrete beams, the effects of the longitudinal tensile reinforcement and the concrete cover on the crack distribution are studied. According to the pattern of the crack occurring, the crack elongation and the crack width, cracks are divided into several groups and analyzed statistically, the crack pattern corresponding to the structral design is determined. The method for calculating the effective influencing area of longitudinal tensile reinforcement (that is the effective area of tensile concrete) is proposed, in which the effective depth of normal section and the effective diameter of longitudinal tensile reinforcement are considered. The statistical analyses are carried out to investigate the average crack spacing, the average crack width and the magnifying coefficient of crack width.