A relatively deepgoing experimental research and analysis is carried out for the reinforced concrete beams strengthened with externally bonded Carbon fiber reinforced plastic (CFRP). First, a total of eight test beams are derived. The four-point bending test is then used to determine the load-displacement relationships of the beams. In the study, the performance of CFRP sheets is investigated. By comparison of the results of the experimental research on the R.C beam unstrengthened and the R.C beam strengthened by CFRP, it is shown that the influence of the carbon fiber sheets on the flexural carrying capacity of the strengthened beams is significant, CFRP has obvious effect to constrain the crack of the beams. The beam strengthened by CFRP at the different stages of the loading has ‘strain lag’. The plane assumption is valid for the beams strengthened by CFRP in different stages. The ductility of the beam strengthened by CFRP is obviously improved.