The semi-circular breakwater has many advantages,such as high stability,simple structure,and convenient construction.In previous research on the reliability of this type of structure,wave loads of breakwater were calculated through the wave height and period,which were regarded as stochastic variable.Estimating the probability distribution models of the above parameters,then the explicit limit state equations can be established and solved.It should be noticed that,for the sequence of wave loads calculated,the dispersion degree of the optimal distribution is poor.Thus,this paper proposed a method of reliability analysis of breakwater based on implicit performance function.Wave height and period are regarded as stochastic variables without the needs of constructing wave loads which are considered as intermediate variable sequence.It is able to avoid the error and simplify the calculation process by this approach.Both the explicit and the implicit methods are applied to calculating the reliability of the semi-circular breakwater.The results show that the difference of the reliability indexes by these two methods is caused by the fitting error for wave load distributions.