The conventional core analysis conducted interiorly usually could not give the oil flowing performance in the process of water-flooding and the distribution of residual oil at the end of water-flooding. However, with Nuclear Magnetic Resonance (NMR) T₂ relaxation spectrum, the oil movement in porous media and the distribution of remaining oil could be directly observed. Some core samples which had different permeability levels were chosen to conduct displacement experiments. The results show that for the cores with low permeability, the oil in the big pores will be displaced easily and the breakthrough recovery is high. Increasing displacement pressure is also able to further enhance the final oil recovery. Therefore, in the development process of these reservoirs, injecting water will be reasonable and realistic and is able to obtain better result. However, exorbitant displacement pressure might change the distribution of residual oil, that is, some parts of oil will be driven into the smaller pores and will become harder to be developed in the future. When the experiments have been completed, some of oils are still found in all sizes of the pores, including the big ones. For the cores with ultra-low permeability, breakthrough recovery is very low compared with the cores with low permeability. Therefore, water-flooding displacement is no longer an efficient development mode for these reservoirs. Oil field needs some other techniques, such as acidifying treatment, fracturing work, etc to assist the development of the cores with ultra-low permeability.