  We propose a modified mode-expansion of the bulk fields in a BPS domain wall
background to obtain the effective theory on the wall. The broken SUSY is
nonlinearly realized on each mode defined by our mode-expansion. Our work
clarifies a relation between two different approaches to derive the effective
theory on a BPS wall, {\it i.e.} the nonlinear realization approach and the
mode-expansion approach. We also discuss a further modification that respects
the Lorentz and $U(1)_R$ symmetries broken by the wall.
