Abstract: In the process of calculating probability for large earthquake occurrence， traditional methods often only consider aleatory uncertainty， but epistemic uncertainty is rarely taken into account. This paper takes Brownian passage time (BPT) model as an example， epistemic uncertainty of mean recurrence interval of large earthquakes is analyzed quantitatively by using Bayesian estimation method， and how to take epistemic uncertainty into the calculation of the occurrence probability of large earthquake is also studied. The results show that there is significant difference in parameter uncertainty among different methods for determining mean recurrence interval of large earthquakes， also there is remarkable difference between the results with and without considering the epistemic uncertainty of parameters in the process of calculating the probability for large earthquake occurrence.