Abstract: Based on the mKdV theory of internal solitary waves in a twolayer fluid, a theoretical model for analyzing the interaction of internal solitary waves with tension leg platforms was presented by using coupling motion equations of six degrees of freedom for the floating body combining with the modified Morison formula. The observational data near the Dongsha Island were used as the characteristic parameters of the internal solitary wave, the characteristics of hydrodynamic load and motion response, as well as tension changs of the tethers for the ISSCTLP due to such an internal solitary wave were computed and analyzed. The results show that internal solitary waves will give rise to sudden impact load and motion response with the large amplitude, as well as remarkable increase of the tether tension. Therefore, the influence of internal solitary waves on the hydrodynamic characteristics of the deepsea platforms including TLP can not be neglected in their designs and applications.