Seven specimens were tested to investigate shear strength of reinforced concrete columns strengthened by wrapping carbon fiber reinforced plastic sheet. All specimens were tested under lateral reversal cyclic loading and a constant axial load. The main parameters considered were CFRP sheet amount, shear span/depth ratio and axial load ratio. Many strain gauges were attached to CFRP sheet to obtain its shear contribution. It was found that the shear behavior of RC part of the strengthened column was almost the same as that of the unstrengthened one. The parameters were found to have an influence on the shear contribution of CFRP sheet, which could be explained by truss-arch shear resistance mechanism. A simple superposition method is suggested to calculate the shear strength of the strengthened column, in which a shear coefficient (ν) is proposed to evaluate the shear contribution of CFRP sheet based on the test results. The calculated results of suggested method are shown to be in reasonable agreement with test ones.