Abstract: The probabilistic model of resistance and partial factors of concrete beam given in Unified Standard for Ｒeliability Design of Building Structures ( GB 500682001) are mainly applicable to the common concrete beam， and it lacks full considerations of influences of prestress． To overcome this shortcoming，a refined probabilistic model of resistance was obtained under different amounts of reinforced steel and prestressing tendon，using the Monte Carlo sampling method，as well as combining with the current probabilistic models of all resistant factors and the capacity formulas in codes． Then，the influences of interesting parameters on reliability index were analyzed for prestressed concrete beam． The results showed that the corresponding design reliability indexes were increased largely with the increase of the amount of prestressed tendons，thus the differences from the target ones were underestimated for both seismic combination and non-seismic combination if they were represented by the reliability indexes of the common concrete beam only．