The reliability of mechanical seal has an important influence on the safe and stable operation of nuclear main pump.To achieve the reliability evaluation of the mechanical seal of the nuclear main pump under the condition of zero-failure data,the operating data of the mechanical seal of the Daya Bay nuclear main pump were analyzed,its reliability distribution was determined.A reliability analysis model combining Bayes theory was established,and the zero-failure data was simulated from the determined reliability distribution by using Monte Carlo method.The influence of the value of packets c on the accuracy of E-Bayes estimation and multi-layer Bayes estimation was investigated when the prior distribution was Beta distribution in the case of zero-failure data.The results show that when packets c<8,multi-layer Bayes estimation is preferred,when c>8,E-Bayes estimation is preferred,and when c=8,the average relative errors of both methods reach a lower level and the multilayer Bayes estimation is lower.The research results have guiding significance for the reliability analysis of mechanical seal of nuclear main pump based on Bayes theory in the case of zero-failure data.