Abstract: The paper will give the reliability of bundled bars in R.C. Beams with high strength members based on carrying capacity limited state by AFOSM. The number of bundled bars, the indetermination coefficient of calculation mode, load effect ratio and the material property will be treated as random variables in this paper, combined with the methodology of reliability, the paper will give the reliability indexes by the program of MATLAB. The influences of the HRB500 reinforcement and bundled bars on the reliability of bending capacity of reinforced concrete beams are analyzed. The result show that the influence of R.C. beams with a 2-bars bundle on the reliability of the beam is very large, and the effect of R.C. beams with a 3-bars bundle on the reliability of the beam is small. When the bending capacity of R.C. beams with bundle bars is reduced by about 5%,the R.C. beams with bundle bars have some negative effect on the reliability of the beams, it is necessary to consider the influence when calculating the bending capacity of the beam.