In order to prove the tension mooring system is safe and useful, Japan Marine Science and Technology Center performed the TLP sea test by utilizing the prototype floating platform. The previous papers of this study discussed the design of the tension mooring system on basis of the results of theoretical considerations and model tests, and introduced the outline of the sea test. This paper discusses on the measuring system and data analysis in the TLP sea test and the dynamic response characteristics of the TLP. The tension measuring system which utilizes the combination of conventional chain-guide wheel and compressive load cell was proved to give the varying tensions about twice larger than the theoretically expected ones. The reason of this overestimation is supposed to be that under the static initial tensions, the varying tensions attenuate while going around the chain-guide wheel and then the load cell measures the larger load out of balance. This inference was proved to be true through the direct measurement of the loads of the chain at both sides of the wheel in the second sea test (1987). The significant values of the varying tensions are estimated and compared well with the theoretical values. The horizontal movement of the TLP is another topic in this study. The surge/sway acceleration of the TLP were measured by utilizing the pitch/roll inclination meters. The yawing motions were measured by the monitor TV camera installed on the deck of the TLP.