Abstract: In order to compare the possible influence on reliability index β values of structure in assuming that the load variables are independent or correlated,the normal of tangent plane at one point on the limit state surface is used to determine the β values.The Hasofer-Lind method,which is generally used in Europe for determining the reliability index β of vertical breakwater,is extended in a generalized stochastic space to be applicable to the condition of the horizontal wave force being correlated with uplift.The calcu lation for a practical example of vertical breakwater shows that the values of β obtained by the improved JC method and this new method (extended HL method) are coincided well with the case of correlated variables,and the β value for the case of correlated variables is obviously smaller than that for the case of independent variables.