The invention discloses an evaluation method for determining a backbone grid line of a power grid. The method comprises the following steps of obtaining configuration information of the power grid and determining a bus set and a branch set for forming the power grid; and searching various key lines included in the power grid by adopting a binary particle swarm optimization (BPSO) rule on the basis of various preset operation modes of the power grid, various pre-arranged initial fault lines of the power grid, the bus set of the power gird and the branch set of the power grid to obtain a branch set occupied by various key lines, wherein the branch set occupied by various key lines forms the backbone grid line of the power grid. According to the evaluation method for determining the backbone grid line of the power grid, the key lines included in the power grid are searched by adopting the binary particle swarm optimization (BPSO) rule through the operation modes and the initial fault lines of the power grid, thereby determining the backbone grid line of the power grid.