The invention relates to a hydraulic impactor regulated and controlled by a piston. The upper end of a shell of the hydraulic impactor regulated and controlled by the piston is connected with an upperportion switching joint in a threaded mode; the lower end of the shell is provided with an anvil; the lower end of the anvil is provided with a lower portion switching joint; a cylinder body is fastened in the shell; an upper portion spacing sleeve and an upper valve seat are arranged between the upper portion switching joint and the cylinder body; a valve cover is arranged in the upper valve seat; a passageway is arranged around the valve cover; a valve cavity is formed by the valve cover and the cylinder body; an impact hammer passes through the cylinder body and stretched into the valve cavity; the bottom of the impact hammer contacts with the shell; a low pressure cavity is formed between the impact hammer and the cylinder body; the shell is provided with a low voltage channel, and the a low pressure chamber communicates with a annulus by the low voltage channel; the upper end of the anvil is provided with a valve cylinder; a first piston bottom plate is located in the valve cylinder; the upper end of the anvil is provided with a valve barrel, and the second piston bottom plate is located in the valve barrel; the second piston bottom plate is a free end; the bottom of the impact hammer is provided with a piston groove; and when the piston is connected with the anvil, and a second piston top plate is located in the piston groove. The hydraulic impactor controlled by the piston solves the problem of a poor impact effect of an existing hydraulic impactor.