Abstract: Presented in this paper are the results of experimental study and analysis of liquefaction characteristics of clayey sand .The laboratory tests on soil samples after prepared with the same dry density and different clay mineralogical composition and different content of clay particles were so as to determine the main parameters which affect the liquefaction behaviour of clayey sand .The tests were performed run on DSD-200 type dynamic triaxial device. X-ray diffraction analysis was also performed. By comparison of the obtained data, the following conclutions are drawn out: (1) the liquefaction-resistant characteristic of clayey sand varies with different clay mineralogical composition; (2)the relation between the dynamic shear strength and the clay particles is not monotonous, but is parabolic and a regression equation for the parabola is given presented by the authors;(3)when the clay particle content is between 8.5～9.5%, the clayey sand is weakest liquefaction-resistant.