The solution to high-speed-railway seismic source function is of great theoretical significance for the inversion of high-speed-railway focal mechanism, propagation law and energy evolution, which may provide a reference for the seismic exploration of rock mass structure in shallow ground. In this paper, the simulation signal characteristic is studied through MATLAB, by working out the Green function of high-speed ailway seismic source in near-field and proceeding forward calculation. Based on the comparative analysis of simulation signal and measured data, the Green function is verified. In addition, wth further analysis of vibration curves, frequency-spectrum diagrams and energy distribution maps, the results show that in the near-field of high-speed railway seismic source: The seismic signal is broadband, of which the vibration differences at each observation position in the horizontal direction indicate the propagation law of high-speed railway seismic wave, while the energy attenuation characteristic can be reflected by that in the vertical direction; There are clear discrete spectral lines in high-speed railway seismic wave, of which the feature frequency varies from 60Hz to 370Hz, affected by the propagation distance; The spacial energy distribution of high-speed railway seismic wave radiation in near field depends on the frequency response property at the seismic source, and the frequency response property shows significant difference with the frequency ranging from 40Hz to 500Hz.