Abstract: A brief introduction to the design concept of underwater walking & swimming robot is provided in this paper. And based on the computational fluid dynamics (CFD) method, a hydrodynamic numerical simulation model for the robot body is established. Then the flow field under different body inclination conditions and different ocean currents is numerically simulated by ANSYS Fluent, and the curves of resistance, lift and pitching moment with inclination are obtained. At the same time, the stability analysis method for underwater walking &swimming robot is established by combining dynamic stability margin method (DSM), and the stability of the walking &swimming robot is analyzed. The stability of the tilting activity threshold is obtained under different inflow environments.