A six degree of freedom numerical simulation model of unmanned underwater platform is established, which is suitable for large angle of attack. In addition, quaternion-based platform attitude model is adopted to substitute the traditional Euler- angle form so as to eliminate singular phenomena of motion equation under some special circumstances, namely platform attitude changes in large amplitude or some specific uncertain Euler-angles. On the basis of correlation theory of elastic mechanics, an elas- tic-plastic numerical seabed model which complies well with actual seabed physical characteristics is established, Combining the bot- tom-seated platform-seabed interaction with the platform’ s space motion model, the motion response of vertical platform bottom- seated mooring to ocean current effect is predicted, and the bottom-seated stability of platform is analyzed to provide references for subsequent design.