Abstract: A rapid and reliable dynamic backcalculation procedure for estimating material properties of plate on layered viscoelastic halfspace foundation through the data measured from in-situ Falling Weight Deflectometer (FWD) tests is presented. A simplified semi-analytical method using spline functions is proposed for evaluation of flexibility coefficient matrix of layered elastic foundation, and the plate is modeled by thin-plate finite element. Equilibrium and compatibility conditions are enforced at the soil-plate interface. Furthermore, a system identification method is used in conjunction with the proposed procedure for estimating material properties from dynamic responses of plate, and the analysis is based on frequency domain fitting. Numerical results show that the proposed method is effective and promising.