In this paper, Ni-Co compositional coatings were electrodeposited by brush-plating and the surface topography images were obtained with the help of scanning electron microscope. The surface topography of Ni-Co coating and the Co element in Ni-Co alloy coating were changed by changing the proportion of Co in plating solution. The fractal dimensions of the surface topography of Ni-Co coating with different Cos were counted based on gray image fractal theory. The impact on the surface topography of Ni-Co coating by the proportion of Co element in plating solution was studied by fractal dimension.