Summary: A robust optical flow algorithm for larger motion velocity and larger velocity change under large varying illumination is presented. A general linear brightness model is embedded in the gradient constraint equation, which improves algorithmic stability under large varying illumination. The anisotropic diffusion equation is introduced in the spatial oriented smoothness constraint, so that it can improve the computation of flow velocity in the motion discontinuities, according to these improvements, the differential optical flow algorithm based on multi-scale-space focusing is used. An invariant energy function under the linear variation of scales is obtained by normalizing the parameters. Motion compensation is introduced to iterative process, and then the error of brightness is decreased. The experimental results show that the algorithm proposed in this paper provides with good computation accuracy for lager motion velocity and larger velocity change, and the flow field of 100% density can be created.