The influence of spatial variability of rockfill materials on the dynamic stability of dam slope of rockfill dams was studied. Under the framework of Monte Carlo method, the random finite element method (RFEM) based on the local average subdivision method was adopted to simulate the seismic response and analyze the slope stability of a high concrete face rockfill dam in Xinjiang, China. By comparing the calculation results using the RFEM and conventional deterministic finite element method, it is determined that (1) when the spatial variability of the rockfill materials is considered, the number and dimension of sliding bodies, together with sliding movements and duration increased; therefore, the overall risk of the dam slope is significantly higher than that when the spatial variability of rockfill materials is not considered and (2) the dynamic safety indexes of dam slope are sensitive to the spatial variability of rockfill materials and show high degree of discretion consequently.