In order to achieve accurate bottom sowing for patinopecten yessoensis seedlings, ensure more reasonable aquaculture capacity, and solve the problem that the current counting and statistics work is still based on labor, with high labor intensity, low work efficiency and high counting error, a new counting device for patinopecten yessoensis seedlings based on STC89C52 chip-microcomputer and light screen sensor was designed. The device can realize automatic queuing, data count collection display and printing. Results showed that: In the first phase, the optimum technological parameters of the device were determined by the orthogonal test; and in the second phase, a 15-group of comparative tests were executed based on actual production situation. The results showed that the average accuracy of counting and statistics was 99.6%, and the working efficiency was 2.49 kg/ (person · min) , which was about 1.73 times of the manual counting and statistics. It was showed that the counting device for patinopecten yessoensis seedlings has the advantages of high accuracy, stability and high efficiency, thus having good prospects in practical application.