The invention discloses an apparatus for testing welding restraint stress. The apparatus comprises a first supporting member, a second supporting member, a stress bearing assembly, and a stress measuring assembly; a first welding sample is connected to the symmetry center of the first supporting member; a second welding sample is connected to the symmetry center of the second supporting member; the portions to be welded of the first welding sample and the second welding sample are close to each other; the stress bearing assembly is connected between the first supporting member and the second supporting member in a stress-adjustable manner so as to deform correspondingly when bearing the welding restrain stress; and the stress bearing assembly is symmetrically disposed with respect to the symmetry centers of the first supporting member and the second supporting member; and the stress measuring assembly is connected to the stress bearing assembly and is used for outputting the welding restraint stress borne by the stress bearing assembly. The present invention also discloses a method for testing weld restraint stress. With the apparatus and method for testing welding restraint stressof the invention adopted, the welding restraint stress borne by the welding samples can be accurately acquired during a welding process, and the magnitude of the welding restraint stress borne by thewelding samples can be controlled.