Abstract: Based on the data for designing concrete structures as well as the statistics of sectional geometry and the mechanical properties of the materials involved, the design formulae for determining flexural capacity of concrete beams reinforced with fiber reinforced polymers (FRP) rods are proposed firstly. Then, the Rackwitz-Fiessler method is applied to calculate the averaged reliability index of six load effect ratios for flexural capacity. After the study of the effect of the partial factors of FRP rods on the averaged index, the partial factors of 1.25 for GFRP rod and CFRP rod are suggested in the end. The reliability analysis indicates that the over-conservative partial factors of FRP rods can only result in concrete crushing in high possibility. The application of those factors would cause a great waste because the reliability level corresponding to that failure mode is almost independent of the partial factors of FRP rods. Design failure mode and actual failure mode do not always occur in unison. The range of their potential unison would increase as the partial factor of FRP rod increases.