The invention discloses a pump-pipe fixing method for downward ultra-deep composite pumping of concrete. A first pumping device is arranged at the top of the cliff, a second pumping device and a buffer device are connected in the middle of the cliff, and the buffer device is connected with the first pumping device via a first pump pipe. The second pumping device is connected to the construction area located at the bottom of the cliff through the second pump pipe, and the second pump pipe is fixed to the cliff by the fixing means. The fixing means comprises a support plate, a second buffer spring, a buffer plate, a hoop, and a diagonal support, wherein the buffer plate is fixedly connected to the top of the second buffer spring, the middle of the buffer plate is provided with a second through hole corresponding to a first through hole, the hoop is fixedly connected to the upper surface of the buffer plate in the positions corresponding to the first through hole and the second through hole, and the second pump pipe is penetratingly arranged in the hoop; the diagonal support is provided at the bottom of the support plate. The buffer plate can slow down the impact of the second pumping device on the fixing device and prolong its service life.