The invention discloses an automatic piano adjusting device for vocal music performance and an adjusting method of the automatic piano adjusting device. The automatic piano adjusting device comprises a piano frame, piano keys and a top cover hinged to the top of the piano frame, wherein peripheral plates are arranged on two sides of the piano frame and located on two sides of the piano keys, slide rails are arranged in the peripheral plates, a level gauge is arranged on the surface of the top of the piano frame, an air cylinder is arranged on the right side of the piano frame, a support frame is mounted at the output end of the air cylinder, the other end of the support frame is mounted at the bottom of the top cover, a horizontal platform is glidingly connected to the peripheral plates, a pedal device is arranged at the bottom of the horizontal platform, piano feet are arranged at the bottoms of the piano frame and the horizontal platform, and electric telescopic poles are arranged on the piano feet, so that the included angle formed between the piano frame and the top cover can be automatically adjusted. The horizontal height of the device can be automatically adjusted under the combined action of the level gauge and the electric telescopic poles. The automatic piano adjusting device has the advantages of being reasonable in structure design, simple to operate and the like and can rapidly and effectively adjust the piano device for vocal music performance.