The analytical expressions of reliability indices such as LOLP, LOLF and EDNS, with respect to component reliability parameters, are firstly presented in this paper, and then the actual physical meanings of the coefficients K1~K4 and D1,D2 in these analytical formulas are detailed. Based on these analytical formulas, a full set of sensitivity formulas of reliability indices with respect to component reliability parameters are deduced. Utilizing these analytical formulas, we can not only easily calculate the system reliability indices accurately in an analytical mode when component reliability parameters vary, but also obtain the function curves of the system reliability indices versus the component reliability parameters. The proposed method can effectively alleviate “calculation catastrophe” and provide an advanced technique to promote the engineering application of bulk power systems reliability assessment. Furthermore, using the sensitivity formulas we can effectually identify system “bottlenecks” and get important guide information for power system planning and operation.