The purpose of this paper is to predict mechanical behavior of degraded cement paste beam due to calcium leaching. Since nature leaching is a slow process, the accelerated experiment has been performed by using a 6 mol/l ammonium chloride solution. At specified leaching durations, three-point bending test was performed on the sound and leached beams with different W/C ratios as well as different fly ash contents. After that, to obtain more information on the mechanical behavior of the beam, leaching depth measurement and elastic modulus test were performed. Based on the residual rate of elastic modulus obtained from the experimental data, the relationship between the loss of flexural strength and the leached ratio was constructed by a simplified model. Finally, the influence of the residual rate of flexural strength on the prediction was discussed, and the best fitting curves were presented.