The invention discloses a classified net-cage fish cultivating method. The method comprises the following steps: 1, providing an inner net cage and an outer net cage, wherein the inner net cage is positioned at one corner of the outer net cage, the mesh diameters of a top wall and a bottom wall of the inner net cage are 3 to 7cm, four side walls are watertight, the inner net cage is partitioned into three layers of box bodies through two interlayer plates, the mesh diameter of the first interlayer plate from top to bottom is 0.2 to 0.3cm, and the mesh diameter of the second interlayer plate is 1 to 2cm; 2, stocking fish fries in the outer net cage; 3, when the chest circumference of each fish fry does not reach the mesh diameter of the inner net cage, adding fish feeds into the inner net cage, when the chest circumference of a certain fish fry exceeds the mesh diameter of the inner net cage, adding the feeds into the outer net cage for 20 to 30min firstly, then adding the feeds into the inner net cage for 2 to 3min, and pumping water by using a water pump every day, so that water flow which flows from top to bottom is formed in the inner net cage. According to the classified net-cage fish cultivating method, fishes of different body types can be effectively separated, and the possibility that smaller fishes are attacked is reduced.