The invention provides an air supply device which comprises a plurality of vertical pipes and a fixing mechanism arranged among the vertical pipes. The fixing mechanism is arranged on the upper portions of the vertical pipes and is of a frame structural mode, and the tops of the vertical pipes are communicated with a high-pressure fan. A method for cleaning a bridge drilled pile head through the air supply device comprises the following steps of (1) placing the air supply device down to a designated elevation position in a steel casing; (2) enabling an air supply pipe and the high-pressure fan to be communicated and starting the high-pressure fan; (3) pumping out concrete which loses efficacy in the steel casing through a slime pump; and (4) carrying out secondary cleaning on concrete in the steel casing manually. The air supply device is simple in structure; the function of supplying air to the concrete in the steel casing is achieved through the vertical pipes, and smooth air supply is guaranteed. According to the method, the high-pressure fan supplies air through the vertical pipes of the air supply device, and therefore setting of cement in the steel casing is prevented, and the cleaning method saves time and labor.