A device for testing corrosion of welded pipe under stress state and a testing method for the same belong to the field of testing and analyzing a material by the means of testing the chemical or physical property of the material. In the device, a partition board is arranged in the middle of an electrolytic cell to divide the electrolytic cell into an electrolytic cell part and an electrode arrangement chamber; a trough circular hole, the edge of which is embedded with a rubber sealing ring, is arranged on the partition board; a bracket is arranged at one side of the electrode arrangement chamber; the bracket is provided with a stress ring, the two ends of which are provided with nuts; the two ends of a work electrode are connected with the stress ring through screw thread and are fixed within the stress ring under the loading state; the lateral of the electrode arrangement chamber is provided with a holding down bolt; and the loaded electrode is tightly pressed against the circular hole embedded with the rubber sealing ring. The invention also discloses a method for testing corrosion of welded pipe under stress state. The invention can be applied to the electrochemistry testing field for testing erosion, corrosion, or anti-corrosion performances of the electrodes with complex shapes and different stress loadings due to different heat treatment conditions.