Yb∶YAG surface gain ceramic slabs have ion diffusion behavior during sintering,which results in a change in the refractive index of the diffusion region,causing wavefront distortion.In this paper,the diffusion theory is used to establish the ion concentration distribution and refractive index spatial distribution model of the surface gain ceramic slab.The influence of the diffusion behavior on the static wavefront distortion is analyzed by numerical simulation.Compared with traditional crystal slab,the ion diffusion behavior of ceramic slab has a certain influence on the static wavefront distortion,and the distortion is in the order of λ/10.