The invention discloses an automatic knocking tool for an aluminum alloy pressure vessel and a remainder cleaning method by using the automatic knocking tool. The tool comprises a slewer and a knocking device, wherein the slewer is connected with the aluminum alloy pressure vessel and drives the aluminum alloy pressure vessel to rotate; and the knocking device knocks the wall of the pressure vessel in the rotation process of the pressure vessel so that at least one of the wall of the vessel, interior angle pieces and separation plates can vibrate. Through the aluminum alloy pressure vessel remainder cleaning tool formed by the slewer and the knocking device, the slewer drives the pressure vessel to rotate at a constant speed according to a set speed, the distance between the knocking device and the pressure vessel is constant, the knocking speed is constant, the uniformity of knocking force and the constancy of knocking frequency are ensured in the process, controllability of the knocking force and the knocking speed of aluminum alloy pressure vessel remainders is realized, and thus both the cleaning quality and reliability are very high.