A wet grinding sanding machine for fine granular material was designed. It consisted of three parts, including stirring grated agencies, cooling system, material handling system. Rotor and its rod pin were whole cast structure with low cost, conical rod pin improved bending strength. Annular space between the cylinder and the cylinder liner formed cylinder cooling water channel, connected with inlet pipe and return pipe respectively. Hollow spindle, inner pipe, pipe joint and rotor cavity formed rotor cooling water channel, so double cooling effect was good. Shell was fixed to the cylinder; turning the handle nut, interaction between the thread and the external thread on the piston forced the pistons to move axially, to adjust the working volume and pressure of grinding sanding machine.