The typical reliability analysis methods are introduced.The performance function is defined and extreme value distribution theory is discussed.The conversion massed of the armour blocks are derived from the Qinhuangdao hydrologic database.The extreme value distribution theory is adopted to fit the conversional armour block mass.It is found that lognormal distribution fits well of the conversional armour block mass distribution.From the case study,the reliability index computed by Monte Carlo simulation method is less than the index computed by JC method,but both less than the value specified in the standard.In Monte Carlo simulation method,reasonable simulation time is recommended.