This paper investigated the issue of fluid-structure interaction (FSI) for fixed offshore wind turbines. The model for a 5 MW monopile wind turbine built by the National Renewable Energy Laboratory (NREL) was selected as an example. The stochastic inflow turbulence code written by NREL-TurbSim, the Kaimal spectrum and exponential wind profile were used to generate stochastic and full field turbulent wind. The aeroelastic code FAST developed by NREL was then used to calculate the aerodynamic load on the wind turbine. The time histories of shear force and bending moment at the top of the tower were obtained. The random wave was simulated using the Pierson-Moskowits spectrum through the harmony superposition method. Two cases were considered in this study, namely, the case that considered the effect of FSI and the case in which the effect of FSI was neglected. Kinematic equations and numerical models under the two cases were developed respectively, and the comparison between the two cases was made to investigate the effect of FSI. The results indicate that distinct deviations affected by the intensity of the wind and wave exists in both wave force and dynamic responses in the two situations.