Abstract: The technique of strengthening concrete structure using prestressed CFRP is one of prime focuses of the strengthening structure with FRP in recent years due to its ability of efficiently utilization of material strength, of which the reliability of the structure strengthened with prestressed CFRP laminate is a key issue. In this paper the statistical character of design variables of reinforced concrete beams strengthened with prestressed CFRP plates is assessed. Accounting for size and stress gradient effects, Weibull distribution is used to describe the probability distribution function. The loss of prestressed loads is analyzed considering the prestressing method. The probability models of the flexural capacity are established for the three failure models, and the influence of variables on the flexural capacity is also studied. The probability model derived in this paper can be used as the theoretical basis of the reliability analysis and safety assessment of the strengthened structure.