Abstract:The onboard hydraulic oil source system has some fault-free behaviors with normal distributed periods and some faulty ones with exponentially distributed periods. The model of the onboard hydraulic oil source system was built by normal-stochastic PNs which combined firing periods with normal and exponential distribution. A method was proposed for the the firing periods parameters identification, which was the mean value mand the periods standard deviation σfor normal distribution or the exponential distribution mean value μ. The simulation results showed that the computing operating periods parameters were consistent with the real operating periods parameters.