The invention provides a viscous damper based on piezoelectric variable friction. The viscous damper comprises a cylinder barrel, a piston is arranged in the cylinder barrel, the piston is connected with a piston rod, a laminated piezoelectric actuator is arranged in the piston, and the laminated piezoelectric actuator is perpendicular to the piston rod but not intersected with the piston rod. According to the viscous damper, the laminated piezoelectric actuator is arranged in the viscous damper, electric energy can be converted into mechanical energy under a direct piezoelectric effect, in other words, electric current is conducted on laminated piezoelectric ceramics, the deformation quantity of the piezoelectric ceramics is changed, stress acting on friction plates is changed, and therefore the force for pushing the piston rod is changed, the energy consumption of the viscous damper is increased, and meanwhile, additional rigidity can be given to a structure, and the structure is assisted in resisting external loads. The technology has the advantages of high flexibility, high stability, high precision, long service cycle and the like, and can be used for solving the problems that the viscous damper at low frequency is low in energy dissipation capacity and cannot provide extra rigidity for the structure.