Abstract: In order to study the effects of concentration and particle size on filter cake structure of fine coal, vacuum filtration of fine coal in different conditions was carried out, and the porosity and fractal dimension of the cake were obtained by electron microscopy and computer image processing technology. At the same time, the effects of the filter cake structure on filtration dewatering was investigated combined with the filter velocity, moisture content and density of filter cake. The results showed that with the increasing of the slurry concentration, the porosity of the filter cake reduced which led to the lower velocity and higher moisture content and density of cake. On the other hand, the results also proved that the porosity declined and the fractal dimension increased from bottom to top of a cake. And the finer particle size led to greater fractal dimension and smaller porosity. Especially, the porosity of cake was only 5.2% when its particle was -0.045 mm, which brought a lot of difficulties in filtration dewatering.