The invention discloses a method for repairing a steel truss girder lower chord, and relates to the field of bridge construction. The method for repairing the steel truss girder lower chord comprises the steps that S1, at least one construction platform is placed below a steel truss girder, a plurality of first jacks are installed on the steel truss girder, the first jacks and the construction platform are connected through steel strands, and the construction platform is hoisted to a set height through the first jacks; S2, a plurality of correcting devices are assembled on the lower chord, each correcting device is formed by splicing a plurality of profile steel, the correcting devices are of square structures, the lower chord penetrates through the correcting devices, the upper sides and the lower sides of the correcting devices clamp the lower chord tightly, and at least one second jack is arranged on the side, close to a curving bulge of the lower chord, of each correcting device; and S3, the second jacks jack the lower chord transversely and repeatedly, and repairing of the lower chord is completed. According to the method for repairing the steel truss girder lower chord, the lower chord can be repaired rapidly when bridge railway traffic operates and a lower route is normal in navigation, the practicability is strong, operation is simple, and the construction efficiency is high.