The invention discloses a welded steel plate stress detection device, and relates to the technical field of the steel plate stress detection. The welded steel plate stress detection device comprises aworkbench, a support seat is fixedly arranged at a bottom surface of the workbench, and a box body is fixedly arranged at top surfaces of two ends of the workbench; a fist cylinder is embedded at thecenter of the bottom surface of the workbench, a first piston rod is arranged at a top end of the first cylinder, a support block is fixedly arranged at the top end of the first piston rod, two endsof the first cylinder are located at the workbench, and the top surface of the workbench is fixedly connected with two support plates. The welded steel plate stress detection device can detect the stress at the entire welding part of the welded steel plate by improving the welded steel plate stress detection device, the adaptability of the stress detection device can be increased to a large extent; and meanwhile, the welded steel plate can be prevented from breaking through the specific detection on the welded steel plate, and then the loss caused by the breaking of the welded steel plate is reduced.