A hydraulic piston resetting tool for a disk brake includes a main body, a first pressing plate, a second pressing plate and a holding pole, wherein, one side of the main body is connected to the first pressing plate, the second pressing plate is adjacent to the other side of the main body, and the holding pole is connected to the front end of the main body. The inside of the main body is pivotally configured with a first cylinder barrel, the inside of the first cylinder barrel is pivotally configured with a second cylinder barrel, and the inside of the second cylinder barrel is pivotally configured with a stopping piece. The stopping piece is connected to the second pressing plate. The stopping piece activates the reciprocating displacement of the second pressing plate.