The invention discloses a lightning shielding performance assessment method for a 750kV power transmission line, and the method comprises the following steps: 1), obtaining 750kV power transmission line information for lightning shielding performance check; 2), dividing the span of the 750kV power transmission line into a plurality of segments, and obtaining the relative geometric position information of a grounding line at each segment; 3), giving the geographic information of the 750kV power transmission line; 4), dividing the phase of a working voltage of a conductor in the 750kV power transmission line into a plurality of segments, and obtaining the lightning shielding trip-out rates of all line segments at different phases of the working voltage of the conductor; 5), determining the lightning shielding weak points of the power transmission line according to the lightning shielding trip-out rates of all line segments at different phases of the working voltage of the conductor, and completing the lightning shielding performance assessment of the 750kV power transmission line. The method can accurately assess the lightning shielding performance of the 750kV power transmission line.