The vortex-induced motions (VIM) of bluff bodies and multi-column structures has been studied extensively through experiments and numerical simulations. Nevertheless, most numerical simulations ignore the existence of free surface and treat it as a rigid plane using boundary conditions. The objective of this paper is to investigate the effect of free surface on VIM for the Reynolds number covering 1.0×105 < Re < 1.6×105. The two degree-of-freedoms (DOF) vortex-induced motions of a circular cylinder with and without free surface are investigated with our in-house solver naoe-FOAM-SJTU. The Delay Detached-Eddy Simulation (DDES) approach is used to simulate the turbulent flow. To capture the free surface, the Piecewise Linear Interface Calculation (PLIC) which is a geometric Volume of Fluid (VOF) method is adopted. The results show that the free surface has major effects on the in-line motion amplitude, transverse oscillation frequency and motion trajectory, which cannot be ignored.