Plate motion is a remarkable Earth process and is widely ascribed to two primary driving forces: slab pull and ridge push. With the release of the first- and second-order stress fields since 1989, a few features of tectonic stresses provide strong constrain on these forces. The observed stresses are mainly distributed on the uppermost brittle part of the lithosphere. A modeling analysis, however, reveals that the stress produced by ridge push is dominantly distributed in the lower part of the lithosphere; Doglioni and Panza recently made an in-depth investigation on slab pull and found this force cannot be in accordance with observations. These findings of ridge push and slab pull suggest that there needs other force to be responsible for plate motion and tectonic stress. Here, we propose that the pressure of deep ocean water against the wall of continent yields enormous force (i.e., ocean-generated force) on the continent. The continent is fixed on the top of the lithosphere, this attachment allows ocean-generated force to be laterally transferred to the lithospheric plate. The net effect of this force pushes the lithospheric plate. A semi-analytical model shows that this force may combine collisional force, shear force, and basal friction force to form force balance for the lithospheric plate, consequently, the African, Indian, South American, Australian, and Pacific plates obtain a movement of 4.52, 6.09, 2.11, 3.52, and 6.62 cm/yr, respectively.