To establish a 3D metro train-FST coupling model in the frequency domain， the key problem of the rail displacement at each moving wheel-rail contact point caused by all moving wheel-rail forces needs to be solved firstly. The matrix of the TFC establishes the relationship between them. Based on the established 3D discrete supported floating slab track model in the frequency domain， a method to calculate the TFC is put forward in this paper. Based on the relationship between the fixed and moving coordinate systems， the TFC to a moving point on FST can be written as the integration of the rail displacement response at a fixed point in the frequency domain caused by a moving harmonic load. After calculating the TFC of the 3D FST， some conclusions are obtained. At each excitation frequency， the TFC of a moving wheel-rail force to each wheel-rail contact point is the largest at the point of the force itself. Due to the moving of the wheel-rail force， there is a certain difference between the TFC of the front axle wheel-rail force to the rear axle wheel-rail contact point and that of the rear axle wheel-rail force to the rear axle wheel-rail contact point. In the same bogie， the TFC of the left wheel-rail force of the front axle to the right wheel-rail contact point of the same axle is similar to the TFC of that force to the left wheel-rail contact point of the rear axle. It is advisable to use a 3D model to finely analyze the dynamic characteristics of floating slab tracks.