Abstract: A fluid-structure coupling model for autonomous swimming of the flexible biomimetic robotic fish was es-tablished based on the principle of coupled Eulerian Lagrangian (CEL) method，aiming to investigate the influence of the design parameters (fish stiffness，fish swing frequency and fish swing amplitude) of the flexible biomimetic robotic fish on its cruising speed，and to obtain the parameter combination of the bionic robot fish when it reaches the optimal cruise speed． The design parameters of different combinations were obtained by orthogonal test，and the cruise performance of flexible biomimetic robotic fish under different parameter combinations was simulated by nu-merical simulation． The influence of various design parameters on the cruise speed of flexible biomimetic robotic fish was calculated according to the simulation data，and accordingly the better parameter combination was ob-tained． The results show that the CEL method can consider the flexible deformation of flexible biomimetic robotic fish during swimming，so it can more truly reflect the swimming behavior of flexible biomimetic robotic fish in actual situation． In the sample range，the cruise speed of flexible biomimetic robotic fish model increases first and then
decreases with the increase of fish body stiffness and fish body swing amplitude，and it increases with fish body swing frequency． When fish body stiffness (elastic modulus) is 30 MPa，fish body swing amplitude is 0. 13 times longer of fish body and fish body swing frequency is 5. 16 Hz，the cruise speed of flexible biomimetic robotic fish reaches a high level．

Key words: flexible biomimetic robotic fish, fish body stiffness, cruising speed, coupled Eulerian Lagrangian (CEL) method