A fractional derivative model is developed for predicting ground vibrations from high-speed trains. In order to determine the order of fractional derivative of each soil layer, on the premise of the maximum strain of the ground are <3% and the strain linearly change as time approximately, a linear strain hypothesis is put forward. The function of damping with fractional derivative is proposed by simulating the Binghamton model. The order of fractional derivative of each soil layer can be obtained by using Riemann-Liouville fractional derivative and curve fitting. Considering it is complex and difficult to calculate when the different fractional order existed in motion equations, a generalized damping energy is defined in order to acquire a equivalent order of fractional derivative. In the last, the Sweden’s X2000 high-speed passenger train is taken as the object, the feasibility of the proposed method is demonstrated by comparing with the experimental data.