[Abstract] For the purpose to overcome the big limit of DAA that is only being applicable to semi-static fluid-structure interaction problem, nonlinear Doubly asymptotic approximation method is propsed. The method is applied to the computation of transient FSI problem of a moving submerged body. The pressure-time curves are analyzed at different horizontal initial velocity coefficient, and the effects of nonlinearity to the fluid pressure at earlier, intermediate and later times is studied. The change of nondimentional unit-area impulse is invegated along with the horizontal initial velocity coefficient.Finally, the initial velociy condition where nonlinear effect is unneglectable is given, further to give the applicability of the NDAA.