Abstract: In order to solve the problems of large amount of manpower, low efficiency and low accuracy in fry counting in the process of fry breeding, a fry counting device based on video analysis technology was designed. Firstly, the air in the equipment is pumped out by the air pump to create pressure difference between the water surface of the fish pond and the equipment, so that the fish fry and water to be tested enter the equipment together and flow through the channel in the equipment; the camera in the equipment collects the image of the fish fry flowing through, and obtains the gray image frame by frame; reduces the resolution; corrodes and expands the image; binarizes the threshold image; extracts five columns of pixels, and compared with the five column pixels of the previous frame, if the white pixel becomes black, the number of fry will be increased by 1, and then the piston, connecting rod and floating ball control the air pressure in the device to achieve continuous intermittent counting, and finally get the total number of fry. After obtaining the fry video, the device has fast counting speed, small error and no manual operation, which can save a lot of human resources and improve efficiency.