The stability of platform structure is the basic guarantee of safety operation for floating wind turbine on sea. The paper established the model of whole machine of NREL 5MW of floating wind turbine based on the OC3-Hywind Spar Buoy platform, and adopted the radiation/diffraction theory and quadratic transfer function to analyze the influence of second order wave force on dynamic response of Spar platform with the aid of hydrodynamic analysis software ANSYS/AQWA. The effect of the first order and the second order wave force on platform was compared from frequency domain. meanwhile the slow drift response caused by wind, current and second order wave load and the wave frequency response caused by first order wave force were analyzed from time domain. The results showed that the variation trends of difference-frequency QTF and sum- frequency QTF are generally similar at the same degree of freedom; the second order wave force pressureed on platform is one magnitude less than the first order wave force on platform; the effect of dynamic response of the second wave force on different degrees of freedom is different; the domain dynamic response consists of wave frequency response and slow drift response in which the former is a reciprocating motion with a mean value of zero and the latter is a drifting motion of long period.