This study systematically investigates the soft flutter characteristics of the π -shaped girder and the influence caused by the lower stabilizers based on the numerical simulation method. The reliability of the numerical method is verified by comparing the aerodynamic coefficients of the wind tunnel test and the critical flutter wind speed. The soft flutter characteristics of the girder and the effect of the 1/4 lower stabilizers are analyzed. The mechanism of the soft flutter of π-shaped girder and the influence mechanism of 1/4 lower stabilizers are discussed. The results show that the π-shaped girder has obvious soft flutter characteristics，which is more remarkable under the negative angle of attack. At a certain wind speed，the total energy of the vibrating system first increases and then remains constant approximately. The total energy of the vibrating system significantly increases after adding the 1/4 lower stabilizers，which enhances the critical flutter wind speed of the π -shaped girder and reduces the amplitude；The development and shedding of vortices in the initial design produce the same direction of moment as that of the main girder，which promotes the divergence of torsional vibration. The addition of 1/4 lower stabilizers weakens the scale of vortices on the upper surface and forms a stable negative pressure area on the lower surface，which weakens the promotion of aerodynamic force on torsional vibration and reduces the torsional amplitude. The results can provide a reference for wind resistance design and aerodynamic optimization of the same type of bridge.