Abstract: A series of cyclic biaxial tests under both drained and undrained conditions were performed on dense sand.A statistic code was developed with Fish language to study the evolution of fabric parameters.The relationship between macro mechanical properties and micro parameters such as coordinate number,contact orientation and contact forces could be achieved in this way.The mechanism of induced anisotropy,dilatancy,shear softening and cyclic mobility was discussed from the viewpoint of micro-mechanism.It was indicated that there was compatibility between fabric anisotropy and force anisotropy and no cumulative loss of co-ordination number during cyclic loading.