Low salinity water flooding，characterized by low cost，has become the research focus of the scholars at home and abroad due to the low oil price in the recent years. However，the microscopic displacement mechanism of remaining oil by the low salinity water flooding is not clear. The cores from Tazhong4 paleo-oil reservoir were tested. The remaining oil was divided into four types（block，net，island and membrane type）with the help of CT scanning technique and D-T2 two-dimensional NMR techniques. The production of the four types of remaining oil by the low salinity water flooding was analyzed and verified by energy spectrum experiment. The results show that the block-type remaining oil decreases gradually and the other types of remaining oil increase in the process of formation water flooding. When the low salinity water was injected，the proportion of the membrane-type remaining oil begins to decrease and the proportions of the other types remain the previous tendencies. The results indicate that the low salinity water can promote the desorption of crude oil from the surface of the rock and displace more membrane-type remaining oil，which eventually improves the recovery efficiency.