In Japan, short-span deck slab bridges have been facing deterioration, for example, cross-sectional loss, corrosion of reinforcement, etc. Accordingly, repair works for the deteriorated, particularly damaged slab deck bridges, have been undertaken. The load-carrying capacity of the repaired bridges should be evaluated quantitatively. This study proposed a method for assessing load-carrying performance for short-span deck slab bridges. One repaired slab deck bridge was chosen as a sample. A field loading test using a passenger car yielded slab deflection records; then, a FEM model, which agrees with the measured deflection data, was created. The FEM model is composed of solid elements for the concrete slab deck and beam elements for the reinforcing bars. The material properties include tension softening in the concrete and elastic-perfectly plastic characteristics in the reinforcing bar. Firstly, we calculated the transverse influence lines of the deck deflection regarding the intact condition and the repaired condition. The influence lines clarified that the repaired part of the deck had lower stiffness in terms of bending. Then, the FEM analysis revealed the maximum loading capacity defined by Limit State 1 of the target bridge. Although the maximum load-carrying capacity was 254kN, 15% less than the intact condition, the bridge can carry twice the legal axel load.