The invention provides a valve body assembly. The valve body assembly is arranged on a piston body of an oil-pressure damper. A fluid hole is formed in a valve cover. Oil fluid above the piston body sequentially passes through the fluid hole and a drainage hole, so that the functions of unloading and vibration attenuation are achieved; the situation that in the prior art, the form and location tolerance generated between the valve cover and a valve element when an unloading hole is machined in the side wall of a blind hole of the valve element is affected is avoided; matching precision achieved between the valve cover and the valve element is guaranteed; and furthermore, the valve body assembly is stable in quality and precision performance. The invention further provides a piston unit. The piston unit is applied to the oil-pressure damper and provided with the valve body assembly. The piston unit is stable in quality and precision performance. The invention further provides the oil-pressure damper. The oil-pressure damper is provided with the piston unit and is stable in quality and precision performance.