The invention provides a loading device for testing concrete chloride ion permeability by coulometry. A steel bottom plate is provided with two screw holes; two parallel screws are inserted into the screw holes; an underdraught steel plate, an overdraught steel plate and a top plate which are parallel to the steel bottom plate are sleeved on the screws sequentially; a jack is arranged between thetop plate and the overdraught steel plate; a dynamometer is arranged between the overdraught steel plate and the underdraught steel plate; the steel bottom plate is provided with a convex steel support upwards; the underdraught steel plate is provided with a convex steel pressing head downwards; a overdraught steel plate positioning bolt cap is sleeved on one screw on the upper part of the overdraught steel plate; and a top plate positioning bolt cap is sleeved on the other screw on the upper part of the top plate. The invention also provides a method for testing the concrete chloride ion permeability by the coulometry by utilizing the loading device. The loading device solves problems that the conventional concrete chloride ion permeability testing device cannot apply bending loads on tested pieces, cannot simulate the actual load-up condition of in-service concrete members, and cannot measure the concrete chloride ion penetrability under the condition of the bending loads.