The invention discloses an automatic back scrubbing machine in the field of ablution facilities. A towel roller rotating mechanism of the automatic back scrubbing machine comprises a towel roller shaft, a towel roller motor and a sliding block. The towel roller shaft is arranged on the sliding block by a towel roller bearing; one end of the towel roller shaft is provided with a towel roller driving gear; an output gear of the towel roller motor is meshed with the towel roller driving gear; a towel roller elevating mechanism comprises an elevating motor, an upper shaft, a lower shaft and a guide rail; the upper shaft and the lower shaft are respectively arranged on a backboard by bearing blocks; the upper shaft and the lower shaft are respectively provided with a synchronous belt pulley and are in transmission connection by a synchronous toothed belt; the middle part of the upper shaft is provided with an upper shaft gear; the upper shaft gear is meshed with an elevating driving gear; the sliding block is supported on the guide rail; a supporting surface of the sliding block is matched with the guide rail; and the synchronous toothed belt is fixedly connected with the sliding block. The back scrubbing machine has simple structure and superior performance, not only can automatically scrubbing back, but also can massaging and scrubbing any position in a mode of holding a scrubbing grinding head.