The invention discloses a disk hydraulic brake capable of adjusting automobile brake clearance automatically. In the disk hydraulic brake, an annular space for a sealing ring to move axially is reserved in a sealing ring groove. The cross sections of the space, the sealing ring and the sealing ring groove are approximately trapezoid or V-shaped or triangular; and the sealing ring is pressed by the piston and the bottom of the sealing ring groove and performs static sealing basically. In braking, the piston and the inner ring of the sealing ring are driven by an oil pressure, the deformation resistance to axial movement of the inner ring of the sealing ring is overcome, a force for pulling back is stored, and a braking friction piece is linked to eliminate axial movement space and brake clearance and press a braked part at the same time, and thus, friction brake is realized. When braking is not needed, the oil pressure is withdrawn, and under the action of the pull-back force of the sealing ring, the machine parts and the two space clearances are restored. Thus, when braking is not needed, the machine parts are protected from friction, heating, damage oil leakage and long repair and replace period, and are energy-saving, emission-reducing, low in consumption and safe. The structure of the disk hydraulic brake is simple, and the production cost is unchanged basically.