Tests on dynamic characteristics of good RC beam strengthened by pre-stressed CFRP sheets were carried out. The results indicate that the eigen frequency of the beam increases with the increase of pretension. The relationship between eigen frequency and pretension was derived theoretically, considering some interrelated factors. The frequency influential factor was obtained by curve fitting with the experimental value of first order frequency. The theoretical value of second-order frequency was compared with the experimental value, and it is shown the theoretical calculation results can reflect the trend of experimental data. When the pretension is 0KN, the maximum error between them is 0.173, they are in good agreement.