Abstract A finite-difference simulation method for breaking water waves is developed. The Navier-Stokes equations in finite-difference form are solved by time-marching scheme in an inflexible rectangular staggered mesh system. Ingenious techniques are particularly focussed on the implementation of the nonlinear free-surface conditions so that overturning and impinging waves can be simulated. It is demonstrated that this method is applicable to three water wave problems that involve breaking phenomenon, namely, bow waves of an advancing floating body, a shallow water flow over a bump, and waves on a submergible. The simulated results show fairly good resemblance to the actual nonlinear wave motions including overturning and breaking of waves, occurrence of impact pressure, and generation of vortices.