In order to study the deteriorating mechanism of the structure performance, the resistance of deteriorating structures was described by Gamma distribution which has a character of independent increment, the changing process of load was described by Poisson stochastic process and Bernoulli stochastic process respectively, then, the load-resistance double stochastic process system was established. Also, based on the conception of crossing rate, the new time-varying reliability analysis method for the engineering structure performance was put forward and the expression was calculated. Analysis showed that the new stochastic process model can better describe the degradation of resistance and the load variation process with time, so it can provide the theory basis for the evaluation of existing structures based on the time dependent reliability theory as while as the life prediction.
