The invention provides a power transmission network lightning strike reliability assessment method and belongs to the field of disaster assessment. The method comprises the steps of obtaining lightning strike data of regions in which power transmission lines and substation equipment are located and establishing a power transmission network reliability model; determining index weights in a reliability assessment model; and determining a fault rate of a power transmission network in a lightning strike state based on the index weights. The power transmission network reliability model and the reliability model of the substation equipment are established, the power transmission network component reliability index weight setting based on a complex network theory is provided, and finally a reliability comprehensive assessment model of the power transmission network under a lightning strike disaster is established. The practical lightning strike data is utilized in an assessment process, and moreover, the influence of a weight coefficient on the improvement of the power transmission network reliability under the lightning strike disaster is obtained through sensitivity analysis, so a practical suggestion for the power system lighting protection design is provided according to a computing example result, and the judgment of the reliability of the power transmission network in a lightning strike process can be improved relatively accurately.