The flow distribution of stray current in urban rail transit in the ground makes it intrude into the nearby alternating current (AC) power grid transformer. In order to study the influence of stray current in rail transit on the magnetic bias of substations along the line under different soil characteristics, based on a substation in Shanghai and its nearby rail transit system, CDEGS software is used to establish the coupling simulation model of “urban rail transit-AC power grid substation”, so as to study the influence of stray current on the direct current (DC) magnetic bias of the AC power grid transformer under different concrete-soil resistivity. The distribution curve of soil iso-current density amplitude is used, combined with visualization technology, to display the influence range and flow path of stray current. The results show that there is a big difference in the influence of concrete resistivity and soil resistivity on the spatial electric field distribution of the leakage current of the rail and the DC magnetic bias of the neutral point of the transformer. In the simulation model, the maximum influence range of stray current is 1 421.33 m, and the differential of distribution distance and soil resistivity is used as the influence index of soil resistivity on the flow range of stray current. The maximum soil resistivity is 1.42 m/(Ω?m). When the train moves 500.3 m after 33 s, the soil resistivity has the greatest influence on the DC magnetic bias of the neutral point of the substation, which can reach 0.003 431 A/(Ω?m).