A method using data assimilation (ensemble Kalman filter) to estimate the spatial distribution of ground stiffness within a large area is presented. It is hard to use traditional geologic surveys like standard penetration test and surface wave method to evaluate the uncertainty of the ground. The ensemble data assimilation can be used to assimilate the observations of numerical models and estimate the parameters of a physical system through the Monte Carlo method and the uncertainty of estimate can then be evaluated by ensemble spread. This research tries to carry out the velocity of the elastic wave into assimilation to estimate the parameters and evaluate the uncertainty. In the numerical experiments, the effectiveness of the assimilation method has been verified through the reproduction of observation of wave velocity and the numerical models have been improved by creating an initial ensemble with reasonable correlation length which affects the estimate considerably.