To investigate the edge effect on numerical calculation of nonlinear forces for a moving body in the time domain, a large body motion model with linear free surface condition is developed with higher-order boundary element method. Five numerical formulations are used to compute the nonlinear radiation forces on submerged surging bodies with sharp edge and a small chamfer radius at the edge. It is found that for those bodies with smooth surface, the nonlinear radiation forces obtained by all of the numerical formulations are close to each other, but large disperses exist for the body with sharp edge. Examination on the vertical nonlinear radiation forces shows that the method on momentum change rate is insensitive to the small edge radius even the chamfer radius is zero, but the other formulations diverse when the edge radius approaches zero. It is suggested that for a body with sharp edge, the method on momentum change rate should be used, or to replace the body surface by the body with a small radius at its sharp edge.