The invention relates to a power grid topological structure reliability index-based long-term power grid planning method. The method comprises the following steps of: establishing a system topologicalstructure of a planning scheme, and determining a cut set evaluation index according to a power grid scale and a power grid structure; calculating the number of cut sets, the orders of which are minimum, of the planning scheme, if the order of the cut set, the order of which is minimum, is too low or the number is out of a limit, adjusting the power grid structure, carrying out statistics on loadnode data included in each minimum cut set, and calculating a partition load reduction proportion; comparing a partition load reduction upper limit under relatively large accident conditions specified in Regulations for emergency handling and investigation of electric power safety accidents, if the upper limit is exceeded, adjusting the power grid structure, and otherwise, calculating a minimum cut set cutting load probability value; and synthesizing related data to evaluate the planning scheme and then determine an optimal scheme. According to the method, the influences, on system stability,of conditions such as the grid structure and load distribution are considered, so that evaluation indexes are provided for different planning schemes, and beneficial benefit is provided for power grid planning decisions.