The invention provides a static reliability assessment method for a complex power grid, belonging to the fields of simulation and calculation of a power system. The mutual influence of power grids with different voltage grades is sufficiently considered in the method; the method can be used for calculating the reliability index of a system under different power grid structural ways to provide a relatively intuitive index for balancing the safety and the stability of the system to operating and planning personnel; through the index, the performances of the system under different power grid structures can be quantitatively compared and the weak links of the power grid can be found; therefore, the method is used for improving the power grid planning level and optimizing the structure of the power grid and has higher practical guiding significance and application value.