A method of conical anisotropic rigorous coupled wave analysis for grating and a computing device are disclosed. The method comprises: obtaining a target geometric phase δ′g for the anisotropic-material-based grating; obtaining a slow axis azimuth angle ϕc(x) of the anisotropic-material-based grating according to the target geometric phase δ′g; obtaining a permittivity tensor of the anisotropic-material-based grating, wherein the anisotropic-material-based grating has an ordinary index no and an extraordinary index ne, the anisotropic-material-based grating has a slow axis polar angle θc and slow axis azimuth angle ϕc(x), and the permittivity tensor is based on no, ne, θc and ϕc(x); applying the permittivity tensor into Maxwell equations; obtaining electromagnetic field for the anisotropic-material-based grating by using boundary conditions of at least two layers or sublayers of the anisotropic-material-based grating and Maxwell equations for each layer or sublayer, to obtain a diffraction efficiency for the anisotropic-material-based grating.