In this article, the dynamic responses of offshore deepwater light pier under extreme waves are investigated. According to the codes of harbor hydrology ( JTJ 213—1998), fluid-structure coupling effect is taken into account, comparative analysis is made for the responses with different pile-soil impedances. Results show that pile-soil interaction has great impaction to the response of the pier in open sea environment. When take the pile-soil interaction into consideration, the response of the pier is only 45%~65% of that without pile-soil interaction. The dynamic response of the pier is greater under random wave than regular wave, and the response is much bigger especially with high wave frequency. By these conclusions, the impedance under more realistic two phase saturation medium is advised. For that response will be much bigger when wave frequency close to structure natural frequency, it should be pay more attention when the pier subjected to random wave especially with high frequency.