The invention discloses a process for both reducing sludge and recovering phosphorus. A bioreactor tank body and an upward-floating separator tank body are included in the process; the bioreactor tank body is connected with the upward-floating separator tank body through a connecting pipe; one end of the connecting pipe is inserted to the bottom in the bioreactor tank body from top to bottom, and the other end of the connecting pipe is inserted to one side in the upward-floating separator tank body from the bottom of the upward-floating separator tank body; a pipeline mixer is arranged at the orifice of the part of the connecting pipe in the bioreactor tank body; and the left side of the bottom of the bioreactor tank body is provided with a reactor bottom flushing pipe. According to the invention, secondary circulation is formed in the bioreactor tank body, and biological sludge at the upper part enters a reactor again to participate in a reaction, so formation of scum is prevented; the upward-floating separator tank body overcomes the problem that sludge in a sedimentation basin is hard to separate in subsequent operation since effluent comes out from an upper part in common deep well aeration processes; and the process provided by the invention couples biological sludge reduction and chemical phosphorous removal, so the process is simplified, and phosphorous removal efficiency is more than 90%.