Abstract: In the report, aimed at the equivalent stiffness calculation of the steel truss girders, based on a long-span suspension bridge, the spatial finite element models of the different truss parameters were established. The static finite-element analysis of the cantilever models was performed to calculate the displacement of main beam, the equivalent section moment of inertia of truss was obtained, and the variation trends were analyzed. Based on the calculation data, aimed at the major parameters, the dimensionless formula was performed for fitting. The results indicated that the effects of the different parameters of the major chord member on the equivalent bending resistance moments of inertia can be summed up as the effects of the section area parameters of the main chord, and which increased linearly. However, the effects of the changes of the different parameters of the major chord on the equivalent torsion resistance moments of inertia were different, which could not be summed up as the effects of the section area parameters. Under the different parameters, the values of the equivalent moments of inertia were compared. The results showed that the precision of the fitted dimensionless formula was satisfied, the largest error was less than 5%, which can be used for the calculation of the moments of inertia of truss.