Size effect of reinforced concrete(RC) beams strengthened in shear with U-wrapping carbon fiber-reinforced polymer was investigated by designing two types of similar geometry beams, named large and small beam. The results indicated that the shear contribution of CFRP strips is associated with beam size. CFRP shear contribution of small beam is superior to large beam. Besides, in small beam, calculative CFRP shear contribution is smaller than actual CFRP shear contribution, while in larger beam is opposite. The shear value of CFRP strips increase with the loading level increasing, and the increasing speed in large beam is faster than small beam. At the same loading level, CFRP shear value of large beam is higher than small beam.