In order to solve the problems of precise grading and screening of fish fry and lack of counting device in industrial aquaculture ponds, a rotary live fish grading and counting device was designed for the grading and counting of live fish fry. After the fishes were pumped from the pond to be graded to the rotary live fish grading and counting device by suction pump, the fish fries were classified into three sizes, then the number of fish fries of each size was counted by the counting device in the pipe, and finally fish fries of different sizes were put into their respective aquaculture ponds. Grading sizes can be adjusted by touching the control panel. According to the width of the back of the fish, the live fish that can be graded is 1~30 mm wide in the back, and the accuracy is 1 mm. The grading device is equipped with a frequency conversion motor, and the rotating speed of the rotary device can be adjusted through the touch screen. The adjustment range is 6~15 r/min. Rainbow trout was selected for the experiment, and the width of the fish back was 9~26 mm. The results show that: when the speed is 8 r/min, the maximum deviation is 2 mm; the grading efficiency is 9 600~14 400 pieces /h, the grading error rate is 4.4%~5.5%, and the counting error rate is 2.5%~4.5%. The device can better meet the requirements of simultaneous grading and counting of live fish in industrial aquaculture ponds.