The evaluation of basic characteristics of an ocean wave (including the wavelength and wave profile etc.) has been widely studied by ocean engineers in the past. Conventional investigations for determining the wave characteristics have been based on the assumption of a rigid seabed [Fenton JD, Mckee WD. On calculating the length of waterwaves. Coastal Engineering 1990;14:499-513]. Based on this assumption, the wavelength of a three dimensional short-crested wave system is exactly the same as that of two-dimensional progressive waves and standing waves. In this paper, employing a complex wave number, a new wave dispersion equation will be derived, in which the soil characteristics of the porous seabed are included. It is found from the explicit expression of the new wave dispersion relation, the incident wave angle of the short-crested wave and characteristics of the seabed directly affect the wavelength and wave profile. The damping of a short-crested wave over a porous seabed is also investigated in this study.