The invention discloses a method for evaluating the external insulation level of an old direct-current line. The method comprises the steps of selecting influence factors, determining the weights of the influence factors, evaluating the external insulation level state of the line and determining an evaluation result. Five factors of an external operation environment, an insulator state, an external insulation operation fault, a difference with a current design specification and a difference with a similar line insulation design are selected. The weights of the influence factors of the method are respectively 0.35, 0.3, 0.2, 0.1 and 0.05. The evaluation method provided by the invention provides a feasible external insulation level evaluation method for a DC line with long operation time. According to the method, the general situation that the external insulation level of the old direct-current line is simply judged only through individual factors in the past can be changed, engineeringconstruction can be guided more effectively, and certain economic benefits and social benefits are achieved.