Based on experiments of true micromodels of sandstone, the microscopic manner of water displacing oil and the formative mechanisms of residual oil were observed. The result shows that there are two types of displacement in the displacing process of oil by water: pistonlike and unpistonlike displacements. Influenced by the pore structure and surficially physical features, the unpistonlike displacement dominates in the water wettability reservoirs. The residual oil was mainly formed by the means of by passing, snap-off and wettability transition in pore surface. Among the three mentioned means, the by passing of injected water resulted from heterogeneity of pore structure and capillary Pressure was the most important one. In addition, the experiments proved that because the original pore structure and surficially physical features were well retained, the true micromodels of sandstone would not only improve the reliability of the experiments, but also enlarge the application scope of the micromodels in the field of displacing experiment. Based on experiments of true micromodels of sandstone, the microscopic manner of water displacing oil and the formative mechanisms of residual oil were observed. The result shows that there are two types of displacement in the displacing process of oil by water: pistonlike and unpistonlike displacements. Influenced by the pore structure and surficially physical features, the unpistonlike displacement dominates in the water wettability reservoirs. The residual oil was mainly formed by the means of by passing, snap-off and wettability transition in pore surfaces. Among the three mentioned means, the In passing, the experiment proved that because the original pore structure and surficially physical features were well retained, the true micromodels of sandstone would not only improve the reliability of the experiments, but also enlarge the application scope of the micromodels in the field of displacing experiment.