Subsea wellhead for deepwater production subjects to axial force, lateral force and bending moment under the seismic loading, the effect of subsea christmas tree and casing string’s gravity. Joint action of these forces makes it is possible that horizontal displacement exceeds the limitation and thus loses the stability. A mechanical analytical model of subsea wellhead for deepwater production is established on the basis of the pile foundation theories and material mechanics, the seismic load and behavior between casing string and formation are considered. The analyses on lateral displacement, angular distortion, bending moment and shear force show that the affection of lateral load is focus on the upper section of casing string, and the lateral displacement of subsea wellhead for deepwater production increases along with earthquake load and thus decreases stability. The stability improves notably with the increase of coefficient of soil reaction. Therefore it is necessary to obtain the on-the-spot geological data in shallow formation. The wellhead stability may be improved to different degrees by taking measures such as minimizing axial load, enhancing the conductor bending strenth, increasing the depth of the casing string in soil, reducing the outcropping length of the casing string.