The coefficient of earth pressure at rest of granular soils is revisited by discrete element method (DEM) simulation. The effects of confining pressure, soil density and over-consolidation ratio(OCR) on the are systematically investigated. The coefficient of earth pressure at rest defined in the conventional form and in the incremental form are compared; and the effectiveness of Jaky’s equation and Mayne and Kulhawy’s equation in predicting is examined. The results show that the K0 and generally approach their “true” (or constant) values when the applied vertical stress is 6-10 times and 4 times of the initial isotropic stress. Meanwhile, the value remarkably decreases as void ratio decreases. The OCR has a significant effect on the K0 value and the K0 value is quite different in loading and unloading stages for the same OCR value. Better prediction is obtained by Jaky’s equation and Mayne and Kulhway’s equation if peak friction angle is used, although the prediction may be quite different from the measurement.