Abstarct: Given the importance of strengthening and repairing the structures especially bridges and developing of FRP sheet strengthening method in current years, many researches in the field of structural have had a tendency toward evaluation of FRP strengthening system and comparing it with other modern methods. As you know, all bridges are always subjected to dynamic loads posed by vehicle traffic, so fatigue will significantly influence on the loss of load bearing capacity of bridge girders. FRP sheet strengthening system is one of the most effective methods in strengthening and repairing bridges for fatigue. We investigated the effects of fatigue on RC beams strengthened with different CFRP configurations. Moreover, we compared the loss of load bearing capacity caused by iteration of loading cycles and fatigue phenomenon. baxsed on a number of laxyers and sheet width, the samples were modeled with six different configurations in finite elements software ABAQUS and each sample’s static and fatigue state were analyzed. Fatigue analyze consists of two steps. First, cyclic loading in 50000 cycles and second, static loading was applied on sample. Finally, static and fatigue analyzing results for all samples were compared with each other in load-deflection diagram. The comparisons showed the different effects of fatigue phenomenon on RC beams strengthened with different number of the laxyers and sheet width of CFRP. These comparisons also showed that the effect of increasing the number of the laxyers and the thickness of CFRP sheet in beam strength improvement for fatigue is greater than the effect of increasing the CFRP sheet width and contact area in beam strength improvement.