Abstract: The experimental investigation is first carried out on the fatigue property of notched friction welded joints of 45-carbon steel under constant amplitude loading and the analysis shows that the fatigue life can be expressed as the function of the equivalent stress amplitude Δσ_epv,i.e. N_i=Δσ_eqv^2/(1+n)-(Δσ_eqv)_th^2/(1+n)-2, where C and (Δσ_eqv)_th are the fatigue resistant coefficient and threshold respectively. C and (Δσ_epv)_th are found to follow the log-normal distribution. A ccording the physical meaning and their probability distribution of fatigue resistant coefficient C and threshold(Δσ_eqv)_th in the fatigue life expression, the different fatigue specimen are assumed to be distinguished by the different combination of C and (Δσ_eqv)_th, while the difference between the fatigue specimens leads to the scatter of the fatigue life, so a new method is propiosed to simulate the fatigue test and the probability distribution of fatigue life of notched friction welded joints of 45-carbon steel under the variable amplitude loading and checkedby test results. It is shown that both the simulated fatigue life and the test result of fatigue life of 45 steel notched friction welded joints under the variable amplitude loading follow the log-normal distribution, and the two distributions agree well with each other. Therefore, the proposed simulating method may be applicable in the fatigue reliability assessment of mild carbon nothched friction welded joints under variable amplitude loading.