Abstract: The reliability of structural system about transmission tower has been analyzed based on the theory of reliability in this paper. The equation of safety margin considering buckling failure has been derived. The method of calculation about correlation coefficient among failure modes has been found in various conditions. The reliability of structural system about transmission tower has been calculated in PNET in various conditions. The calculation of reliability index about structural system of transmission tower has been summarized systematically. The reliability of ZM2 transmission tower designed by State Research Institute of Electric Power Construction Network in Beijing has been calculated using the new procedure. The feasibility of the calculation of reliability index about structural system of transmission tower has been confirmed.