Abstract: That the cyclical change of the shape of the mantle produces potential energy force in earth's crust results in crustal movement.When the shape of the mantle changes from sphere to relative flat-sphere,the crust of region of high latitudes of Southern Hemisphere and Northern Hemisphere produces opposite pressure to the crust of the region of low latitudes;When the shape of the mantle changes from relative flat-sphere to sphere due to restoration to a balance of the isopotential surface,the crust of the region of the low latitudes of Southern Hemisphere and Northern Hemisphere produces respectively a pressure to the region of the high latitudes.The motive force of present shift of the continental crust in China results from proceeding still to a balance of the isopotential surface in the mantle in the west of China.