A back clapping machine with chest percussion function includes a casing, a movement mechanism, a clap mechanism, and a buffer unit. The casing includes an outer cover, a rear cover, and a housing space therein, in which the movement mechanism is disposed. The clap mechanism is in the housing space and connected with the front lateral side of the movement mechanism. The buffer unit is in the housing space and arranged to elastically abut against the outer cover and the rear cover therebetween. Thus, the present invention automatically carries out back clapping operation and detects the distance for back clapping, also provides a shock buffering effect, thus achieving a back clapping chest percussion operation through a hand alike structure and preventing pressure ulcer.