The pore water pressure in a seabed plays an important role in the stability of the seabed, and it is generally used to estimate seabed liquefaction induced by oceanic loads. When the principle of effective stress is applied, it can easily be derived that the increase of pore water pressure in the seabed means a decrease of effective normal stress and a higher likelihood of liquefaction. In fact, wave influences the load boundary conditions and pore water pressure boundary conditions simultaneously. On the basis of the liquefaction criterion of pore water pressure, two cases are studied: (1) the case where a different seabed is subjected to the same oceanic load and (2) the case where the same seabed is subjected to different oceanic loads. The relationship between pore water pressure in the seabed, the uplift force induced by the wave, and the possibility of liquefaction is established. The results show that the pore water pressure in the seabed under the wave trough (p < 0) should be used to estimate the likelihood of liquefaction rather than the positive pore water pressure under the wave crest (p >0). In the first case, the uplift force and possibility of liquefaction in the seabed decrease when |p| increases. However, in the second case, the uplift force and possibility of liquefaction in the seabed increase with |p|. In addition, these results are used to estimate the possibility of seabed liquefaction in examples, and the evaluation based on pore pressure is compared with that based on vertical effective stress. This conclusion will be applied for a comparison of the possibility of liquefaction due to pore water pressure between diverse cases.