Asymmetrical rolling is an important way to improve the deformation quality of aluminum alloy sheet as a severe plastic deformation technology. The deformation mechanism in thickness direction is difficult to be analyzed due to the characteristics of multivariable, strong coupling and nonlinearity in asymmetrical rolling of plate. In order to deeply study the deformation in the thickness direction of asymmetrical rolling, a strain calculation model along the thickness direction after asymmetrical rolling is established. The deformation zone is divided into rigid plastic rigid zone according to the kinematic characteristics of rolling process. On this basis, the boundary conditions of the deformation zone are modified, and the stream function method is used to establish the near-real velocity field. According to the minimum energy principle and linearized integration method, the rolling power consumption model is established, the multi-field and multi-parameter nonlinear coupling problem in the calculation process is solved, and the rapid calculation of the boundary model of the deformation zone is realized. Finally, the strain calculation model of asymmetrical rolling is established by combining the velocity components and strain rate components. In order to verify the asymmetrical of the theoretical model, numerical simulation and asynchronous rolling experiments were carried out. Compared with the experimental results, the maximum relative error of the calculation results is 13.44%, and the minimum relative error is 1.33%. The overall calculation time is reduced to less than 1 second. The establishment of this calculation model can provide an important theoretical reference for the quality control and prediction of asymmetrical rolling.