<p>Snake rolling is effective in enhancing material properties, and the equivalent strain derived through experiments and by finite element method is time consuming and inconvenient. Therefore, an equivalent strain calculation model for the snake rolling with different diameters has been established. It broke through the assumption of homogenization in the traditional rolling theory and regarded the rolling reduction induced by the top work roll as an unknown parameter. The rigid-plastic boundary conditions at the inlet of the deformation zone were established on the basis of the motion characteristics of the snake rolling. The metal flow equations within the deformation zone were established based on the flow function method. The velocity field in the deformation zone was obtained by solving the metal flow equations, and the strain rate component was then derived by taking a partial derivative of the velocity field. And then, a comprehensive analytical model containing velocity field, strain rate and power field is obtained. Genetic algorithm is adopted to optimize the total power model to obtain the unknown quantity. Finally, the equivalent strain was solved. Finite element simulations and snake rolling experiments were performed, which demonstrate the feasibility of the model.</p>