This paper is about the low frequency slow drift motion response of Truss Spar platform with small-scale piles in bichromatic waves. A numerical model is established to calculate the wave-body interactions under the second-order frame by utilizing second-order time-domain higher-order boundary element method (HOBEM). The wave loads on small-scale piles are calculated by Morison formula, in which the wave field disturbed by the large-scale structure is taken into account. A mooring Truss Spar platform is simulated by this numerical model, and the numerical results demonstrate that the existence of the small-scale piles may lead to the decrease of the motion response of the platform, while the natural frequency will move to the low frequency. The phenomenon explains that the small-scale piles of the Truss Spar play an important role of damping and change the add mass of the platform, so in order to get the more accurate results of the motion response, the wave loads of the small-scale components are unable to ignore.