Abstract: A new method based on the frequency decrease rate for fast identification of site liquefaction from surface acceleration records was presented.The liquefiable site was simplified as a double-degree-freedom model and the formula for calculating the reduction of horizontal natural frequency induced by liquefaction was attained.And then the lower limit of the frequency decrease rate was derived,and the fast identification method of site liquefaction from surface acceleration records was proposed.The reliability of the method was examined with the actual earthquake records and it indicated that by using the present approach not only the liquefied sites and the stiff non-liquefied sites were identified,but also the soft non-liquefied sites were detected.