Abstract: Based on the reliablity theory,a Method of Calculating the failure probability of the reinforced concrete Colums under the combined actions of bending moment and axial force when the applied laods are time-variant processes are presented.This method is to simplify the non linear frnction by piece linearization of the limit state equation and the use of Gaussian processes.An example is given to illustrate the Opproach,which shows the feasibility to simplify the calculation of the ontorossing rate and shows the stochastic feature feature of the bending moment and axial froce for the reinforced concrete colums.