Abstract: In order to analyze the scattering fields of an underwater metal shell target, we propose a novel accelerating computation algorithm based on the shift operator finite difference time domain (FDTD) method for solving the case of a lossy dispersive medium. The spatial distribution of underwater low-frequency scattering fields of a hollow metal ellipsoid and the propagation properties of the low frequency electromagnetic wave across the rough sea surface are considered by the proposed method. For testing the acceleration performance, we obtain close linear speedup and get an acceleration efficiency of more than 95% through numerical cases.By calculating the radiation fields of an underwater electric dipole, it is shown that the results of the proposed method agree well with those analytic results.Numerical results show that the sea surface affects the spatial distribution of the scattering fields, especially the spatial distribution of electric field. Moreover, we get the propagating velocity of scattering fields which is faster above the sea surface than that below the sea surface.