Abstract: Based on the beam model on Winkler foundation,the finite element method for calculating the horizontal dynamic impedances of single pile in layered soil was set up.The elastic modulus of the layered soil was assumed as random field.The statistics of horizontal dynamic impedances of single pile in layered soil was derived utilizing the Neumann Stochastic finite element method.Furthermore,the statistics of dynamic interaction factors were studied and the statistic expressions of dynamic impedances of group piles were presented.Several significant conclusions were obtained through analyzing the examples.