On the basis of Morison’s empirical formula and modal separation method in estimating the force and torque exerted by internal solitary waves (ISWs) on a cylindrical pile, it is found that the loads exerted by the ISWs change largely in different seasons at the same site of the continental shelf in the South China Sea (SCS) even under the condition that the amplitudes of ISWs are the same. Thus, the effect of a seasonal water stratification variation on the force and torque exerted by the ISWs is investigated, and a three-parameter stratification model is employed. It is shown that the loads exerted by the ISWs depend largely on the wa-ter stratification. The stronger the water stratification, the larger the force and the torque;when the depth where the maximum thermocline appears is deepened, the force decreases but the torque increases;when the width of the thermocline is narrowed, the force increases but the torque decreases. The seasonal varia-tion of the force and the torque exerted by the ISWs in four seasons in the SCS is thus explained.