Freak wave (extreme wave, rogue wave, huge wave, water wall, et al) is extremely large water wave in ocean and may occur all over the sea area. Despite its low possibility of occurrence, such a wave may lead to damage of ships and offshore platforms. Until recently, there was no means to generate a realistic extreme wave appearing in a random wave train. A relatively easy way to generate freak waves is using wave focusing. Along with physical experiments, numerical simulations are useful tools for designing coastal structures as well as for understanding natural hydrodynamic processes in the field of ocean engineering. This work is motivated by the requirement of hydrodynamics laboratories to generate! focused waves and to investigate the survivability of offshore wave energy converters due to focused waves. The purpose of this paper is to demonstrate a CFD approach applied to simulations of focused wave. In this paper, a constrained interpolation profile (CIP)-based Cartesian grid method are proposed for the focused wave generation problems and validated by experiment. Focused waves are generated based on the mechanism of wave focusing in a 2D numerical wave tank. The numerical simulation is performed by the CIP-based Cartesian grid method, which is described in the paper. An improved THINC scheme (THINC, tangent of hyperbola for interface capturing), the WLIC/THINC scheme (WLIC: weighed line interface calculation), is applied as the interface capturing method. To validate the capability of the CIP-based model described in this paper, generation of regular waves is firstly computed and compared with the theory. By adjusting the phases of the linear harmonics components, focused waves are formed at a certain target time and target position. The numerical results are compared with experimental data. All the comparisons are in good agreement. It is concluded that the present model with the aid of the CIP technique can provide with acceptably accurate numerical results on the route to practical purposes.