In the design and production of the bionic squid, the combination of the wrist contraction fin flapping and jet propulsion enables the squid to swim in a variety of motions. In order to study the flapping propulsion mechanism of squid fin, the computational fluid dynamics (CFD) method was adopted to conduct numerical modeling of the biological squid in equal proportion, and to calculate and analyze the hydrodynamic characteristics of squid fin at different flapping angles. On this basis, the effects of different parameters on the propulsion performance of squid fin flapping were analyzed and discussed by changing the parameters of fin proportion and fin shape. The results show that:during the flapping process of the squid fin, there appeared obvious vortex zone and pressure difference on the upper and lower surfaces of the fin. Under the action of the pressure difference, the squid completed the heave movement and horizontal movement; when the proportion of fin in the squid body exceeded 0.3, the heave force and horizontal propulsion force both showed an obvious upward trend with the increase of the proportion of fin, while the change of resistance tends to be stable, therefore, a proper increase in the proportion of fin in the squid body can obtain a higher flapping propulsion efficiency; The transverse lozenge fin had higher propulsion efficiency and lower swimming resistance, which is an ideal choice for the design of the bionic squid. The results could provide a theoretical reference and calculation method for the design and manufacture of bionic robotic squid.