A method for calculating power transmission tower angle steel pressure bar stability strength reduction factor includes the steps: selecting angle steel A with the stability strength reduction factor mN=1; selecting angle steel B with yield strength as same as that of the angle steel A; respectively measuring the areas of the angle steel A and the angle steel B; respectively measuring the maximum bearing capacities of the angle steel A and the angle steel B under the condition of the same slenderness ratio; calculating the stability strength reduction factor of the angle steel B according to a formula phi mN=Nu/Afy. The method is more practical and accurate, and the influence of change of test condition and external test factor on test can be avoided.