Abstract: A cyclic simple shear test apparatus, based on a static simple shear test apparatus which has been developed in Nanjing Hydraulic Research Institute since 1964, is constructed. This apparatus is composed of a simple shear box, an electro-magnetic exciter, the static loading system and the electronic recording system. A sample with diameter of 7cm and height of 2cm is enclosed inside a rubber membrane which is in turn confined by steel rings and is attached rigidly to the end plates. By means of the horizontal loading system the initial shear stress is applied to the sample. The vertical and horizontal loads are applied pneumatically and are controlled seperately by two regulating valves.The base of the simple shear box is connected with the excitor which applies the cyclic shear stress to the sample. The amplitude and the frequency of excitation is controlled by the extra-low frequency signal generator, and the signal generated by the latter is amplified and input to the excitor. The max. exciting force is 120kg, and the frequency generally used is 2~3 Hz. During the test the variation of dynamic shear stress, pore pressure and displacement are measured by the transducers and are recorded by the oscilloscope.This apparatus has been now tested, adjusted, and used to investigate the characteristics of liquefaction of some saturated sand samples. It is shown that this apparatus works fairly well. Furthermore, its construction is simple, and it can be operated easily. Therefore it is concluded that this apparatus may be used to study the dynamic behaviour of the soil either for the practical engineering project or for the research purpose.