The injection of grass carp vaccine mainly relies on manual injection, which has some disadvantages such as high labor intensity, low injection efficiency, non-standard injection location and poor injection accuracy, which seriously restricts the development of aquaculture. This paper analyzes the research progress of fish vaccine injection at home and abroad, and formulates the operation strategy of automatic vaccine injection according to the characteristics of grass carp vaccine injection. By means of the head and tail orientation device, the consistent attitude adjustment of the fry was realized. The light vision sensor was used to realize the fast identification of the belly and the back of the fish and the automatic allocation of the injection station. A rotary fishing rod was designed, and the stress and speed changes in the fishing process were simulated by LS-DYNA dynamic simulation. The technology of flexible fixation and rapid injection of fish body was studied, and the automatic injection device of vaccine was designed to complete a series of actions of flexible press, injection and return in sequence. The technical problems such as the inconsistency of body shape, the automatic assignment of station and the speed matching of rotating fish were solved. Based on the above technology, a continuous automatic injection device for grass carp vaccine was designed, and a prototype for automatic injection of vaccine was developed. Through the production experiment, the young grass carp 100 -120 mm long was selected as the object of automatic injection. The results showed that the output of the automatic injection device was about 900 fish /h. The survival rate of juvenile fish within 3 weeks after injection was 98.3%, which was 4% higher than that of artificial vaccine injection. The research results can realize efficient continuous injection of grass carp seedlings, improve the automation level of aquaculture equipment, and have a reference significance for continuous injection of fusiform fish seedlings, with high application value and economic benefits.