A submerged biofiltration purifying apparatus includes a settling zone being a 3D space having open top, bottom, and two lateral sides; one or more filtering zones coupled to the two lateral sides of the settling zone, and each being a 3D space with open sides and having soft contact media connected thereto; and one or more bubble aeration units connected to bottoms of the filtering zones. The soft contact media allow biological films to grow thereon. The bubble aeration units generate air bubbles that guide sewage to flow toward the soft contact media, so that organic substances in the sewage are adsorbed to the biological films. The soft contact media are arranged at a specific angle for the sewage to naturally diffuse toward two lateral sides of the settling zone and recycle. And, purified water settles in the settling zone again to remove remaining suspended solids to achieve sewage purification.