Abstract: A prestressed steel girder is regarded as composite structure of girder and tendons, and the interactions between them are fully considered. The geometrical nonlinear finite element formulations for both girder and tendon are proposed based on the present girder element. The formulations are simple and straightforward. The experimental results of deflections at the mid-span and quarter span, bottom plate strain of the steel girder, and the tension increment of tendons are in good agreement with the theoretical calculations. This confirms the validity of the present formulation.