Abstract: The actual geotechnical property parameters have obvious randomness. The two-dimensional scattering of the P and SV waves in the sedimentary valleys is studied based on the indirect boundary element method (IBEM) in order to explore the effect of the randomness of the medium velocity and material damping on seismic ground amplification effect of the valley. The Monte Carlo method is used to simulate 30 groups of wave velocity ratio samples and 30 groups of damping ratio samples. Finally the present paper gives the single frequency and spectral results of random response of the valley under P wave and SV wave incidence with different incident angles and frequencies. The results show that the variation coefficient extremum of surface displacement response amplitude is significantly larger than the variation coefficient of velocity ratio, and the effect of velocity ratio randomness on surface displacement is the most significant at system resonance frequency, and the maximum standard deviation of surface displacement can reach 7.168. The variation of the ground motion response in the sedimentary center is more significant at low frequency, but it is the largest at the edge of the sedimentary valley at high frequency. On the other hand, the incident angle has little effect on the variation coefficient extremum of surface displacement response amplitude, but it has a significant effect on the spatial variation of the variation coefficient. Meanwhile, the damping randomness has little effect on the surface displacement at low frequencies, but the effect is obvious at high frequencies, especially at the natural vibration frequency of the sedimentary valley, the effect is most significant.