Abstract: An induced electromagnetic measuring system of steel bar stress was set up and the electromotive force of the steel bar surface was measured under the condition of tension to find a new way of stress testing. The stress-electrical spectrum lines were obtained by changing measurement frequency, the data were processed and the stress distinguishing was formulated by the method of least squares. The measuring mechanism of stress-electromotive force was analyzed. According to the experimental results, while the tensile stress rising, the change of induced electromotive force shows two kinds of variation characteristics, increasing at the first and then decreasing at the high stress level, or increasing continuously, at a fixed frequency value between 100Hz and 600Hz. The induced electromotive force reduces generally with increasing frequency at a fixed stress value. The stress-electromotive force spectrum lines of steel bars rise with the increment of stress levels.