Abstract: According to the structural cause of flexural crack in a simply-supported reinforced concrete slab bridge, how to assess its loading capacity quickly was investigated experimentally. With 5 rectangular RC slab beams as specimens, the destructive tests were carried out the way the multi-stage concentrated load was exerted at both the tripartite points of the span simultaneously. Then, the relationship was obtained, in between the maximum and mean heights of cracks, crack width and loading capacity. An empirical formula is thus fitted by means of regression analysis, with a quick assessment of loading capacity of bridge proposed by cracking characteristics. Comparing the values measured with the assessed results, the feasibility and reliability of the proposed method are demonstrated.