Abstract: Under the influence of stray current as well as chloride ion and external load, the shield tunnel steel easily appear corrosion during its service period. Therefore, a three-dimensional numerical model is established in an electrical as well as chemical and mechanical coupling field. The change rule of segment steel corrosion rate at arch and the steel rust layer distribution form are analyzed. The results show that:1) the steel corrosion rate near the segment outside is larger than that near the inside, the intersection angle between the direction of maximum steel corrosion rate and the circle center line is 0°~52°; 2) the segment steel corrosion rate is related to volumetric strain under loading, and the segment steel corrosion rate in the middle is larger than that in the two ends; 3) when the steel occur depassivation, the steel corrosion rate increases linearly with the potential difference of cathode to anode, and it increases logarithmically with the chloride ion content; 4) under the joint action of three factors, the segment steel rust layer form appear eccentric circle, and the radius size and circular center are related to the non-uniform corrosion coefficient as well as the maximum corrosion current density.