The invention discloses a method for machining a submerged pump impeller. The method comprises the steps that firstly, a three jaw chuck clamps a large outer circle of the impeller, and rough turning is performed on an impeller opening ring, a plane A and a front cover board after calibration; secondly, surfacing adjusting is performed, the three jaw chuck clamps the opening ring, rough turning is performed on a plane B after calibration, drilling is performed, rough turning is performed on a rear cover board and a sealing surface, and rough turning is performed on the large outer circle; thirdly, rough turning is performed on the plane B, boring is performed, the rear end cover and the sealing surface undergo finish turning so as to meet the requirements of a drawing, and chamfering is performed; fourthly, turning is performed on a core rod, the impeller is sleeved in the core rod and screwed through a nut, finish turning is performed on the plane A (1), the overall length is controlled according to the requirements of the drawing, the opening ring and the front end cover (3) undergo turning so as to meet the requirements of the drawing, the large outer circle undergoes finish turning so as to meet the requirements of the drawing, and chamfering is performed; fifthly, checkout is performed; sixthly, a static equilibrium test is performed as the requirements; seventhly, a keyway is inserted; eighthly, checkout is performed; ninth, cleaning, burring, oiling and stockroom entering are performed. The method for machining the submerged pump impeller facilitates machining, ensures machining precision and improves production efficiency, and is suitable for machining of industrial pump impellers.