Metal-magnetic memory detection technology is a new type of non-destructive testing technology, which can identify the early damage of ferromagnetic materials. In order to promote the application of this technology in the field of bridge steel damage detection, the static bending test was carried out for the single U-rib orthotropic steel bridge deck inside the steel box girder, the magnetic signal data of the U-rib web under different load levels were collected, and the stress was obtained by combining with ANSYS finite element software, and the force-magnetic curve of the U-rib web along the height direction and the relationship curve between the stress in the stress concentration area and the magnetic signal and magnetic signal gradient were established, and the relationship between the force characteristic parameters and the magnetic characteristic parameters was analyzed. The results show that along the direction of the detection line, the normal and tangential magnetic signal values of each detection line decrease with the increase of load, and the normal magnetic signal curve fluctuates less than that of the tangential magnetic signal under the same load level, and the distribution is more gentle. The normal magnetic signal of the U-rib web has a “peak-trough” phenomenon along the height direction, which has a good correspondence with the stress distribution, and the stress concentration area can be judged by this phenomenon. The “steep rise” phenomenon of the magnetic gradient K curve in the stress concentration area can be taken as the danger warning signal of the yield strength in the actual engineering component. The μσ-λk curve of the force-magnetic correlation characteristic parameter has a good linear fit, and the stress concentration degree of the stress concentration area can be preliminarily judged according to the curve.