According to the design parameter of NREL 5MW wind turbine,the paper built 3D model of wind turbine and TLP. Based on the algorithm of Block Lanczos and the failure theory of Von-Mises,it used finite element method, ANSYS finite element software and open source software of FAST to study the vibration performance and structure stress of platform under the extreme sea condition by considering the structure damping and inertial load aim at platform dynamic property. The results show that different directions of wind, wave and current load have enormous influence on the strength of platform; the maximum equivalent stress occurs in the margin of bottom plate which is the platform dangerous area; the blade rotation and wave motion can't cause the resonance response of platform.