A time-domain method is applied to simulate nonlinear wave diffraction around a surface piercing 3-D arbitrary body. The method involves the application of Taylor series expansions and the use of perturbation procedure to estab-lish the corresponding boundary value problems with respect to a time-independent fluid domain. A boundary element method based on B-spline expansion is used to calculate the wave field at each time step, and the free surface boundary condition is satisfied to the second order of wave steepness by a numerical integration in time. An artificial damping lay-er is adopted on the free surface for the removal of wave reflection from the outer boundary. As an illustration, the meth-od is used to compute the second-order wave forces and runup on a surface-piercing circular cylinder. The present method is found to be accurate, computationally efficient, and numerically stable.