Effective prediction and evaluation of sheet deformation degree has practical guiding significance for bending forming process and product precision control, and neutral layer offset is an important parameter to measure the degree of uneven deformation in the tension and compression area of bending sheet. In this paper, based on the microelement stress balance condition in the plastic deformation theory and the Yoon2014 yield criterion which can reflect the tension and compression asymmetry of magnesium alloy, the neutral layer offset calculation model in the bending process of AZ31B magnesium alloy sheet was obtained, and the neutral layer offset model was verified by finite element simulation and corresponding experiments. The results show that the model can reliably predict the neutral layer migration phenomenon of magnesium plate. During the bending process of magnesium plate, the neutral layer shifts to the tensile side due to the influence of tension and compression asymmetry. The smaller the Angle after bending, the larger the neutral layer offset. The neutral layer offset is the most obvious when the bending Angle is 90° and the pressure is between 40mm and 47mm.