<p>The internal solitary wave (ISW) represents a frequent and severe oceanic dynamic phenomenon observed in the South China Sea, exposing marine structures to sudden loads. This paper examines the prediction model of interaction loads between ISW and FPSO, accounting for varying attack angles and incorporating ISW theories. The research demonstrates that the horizontal and transverse forces on FPSO under internal solitary waves (ISWs) comprise wave pressure difference force and viscous force, while the vertical force primarily consists of vertical wave pressure difference force. The wave pressure difference force is determined using the Froude-Krylov equation. The viscous force is derived from the tangential particle velocity induced by ISW and the viscous coefficient. The viscous coefficient formula is obtained through regression analysis of experimental data with different ISW attack angles. The research reveals that the horizontal viscous coefficient <i>C</i>_<i>vx</i> decreases as Reynolds number (<i>Re</i>) increases, while the transverse viscous coefficient <i>C</i>_<i>vy</i> initially increases and subsequently decreases with the growth of the Keulegan-Carpenter number (<i>KC</i>). Moreover, changes in wave propagation direction significantly affect the extreme magnitudes of both horizontal and transverse forces, and simultaneously modify the transverse force orientation, while having minimal impact on the vertical force. Additionally, the forces increase with the ISW’s amplitude. For horizontal and transverse forces, a thinner upper fluid layer generates larger forces. Comparative analysis of experimental, numerical, and theoretical results indicates strong agreement between theoretical predictions and experimental and numerical outcomes.</p>