In this paper, a simplified assessment method for the wave-induced liquefied depth in a shallow seabed is proposed. By introducing a weighting factor, both the oscillatory and residual pore pressures were considered in the liquefaction criteria. Normalized charts were presented for a quick and simple evaluation of the maximum liquefied depth as a function of wave and soil parameters. Filly, parametric alyses were performed to clarify the applicable range of this criterion. It is found that the increases of relative density and consolidation coefficient will obviously enhance the influence of the oscillatory pore pressure on the liquefaction of a shallow seabed, as well as reduce the liquefaction potential.