Abstract: In order to recognize the effects of cracked degree and the strengthening parameters on the performance of reinforced concrete beams, 6 T-section pre-cracked reinforced concrete beams strengthened with near surface mounted CFRP sheets were tested. The failure modes, the bending moments and deflections of the strengthened concrete beams were discussed. The results showed that the reinforcements by using the near surface mounted CFRP sheets have an obvious impact on the flexural ultimate bearing capacities. The pre-cracked degree has a few influences on the ultimate bearing capacities and the failure modes of the strengthened concrete beams, but splits in the beams developed by pre-cracked process can produce more deflection of the pre-cracked beams. The more fissures are induced, the larger deflection is. The failure modes of all the beams strengthened with CFRP sheets are the debonding of CFRP sheets from the adhesive layer of epoxy. The bending performance of the strengthened beams can be in a good state if reliable shear strengthening can be assured.