Abstract: The movement of a floating circle collar of a gravity fish-farming cage with two types of mooring system commonly used in practice was studied. The wave forces acting on the collar and the cable are derived by Morison method using the second order Stokes wave theory. The trajectories of the tracing points on the collar were numerically computed and physically measured, respectively. The results showed that in the investigated conditions the wave height had significant effect on the displacement of the collar while the wave period turned out to be of little influence. The vertical displacements were much larger than the horizontal ones. Numerical results agreed well with experimental data, which verified the accuracy of the numerical method.