Offshore low-permeability reservoirs have a low percentage of producing reserves and thus are of great development potential.However，the strong heterogeneity of pore structures in low-permeability reservoirs has resulted in complex fluid mobility and oil -water occurrence characteristics，which makes it difficult to tap the remaining oil potential in low-permeability sandstone reservoirs at the development stage. The full-aperture pore size distribution characteristics of low-permeability sandstones and their influence on fluid mobility and occurrence characteristics of remaining oil were investigated by using nuclear magnetic resonance displacement experiments supplemented by high-pressure mercury injection，micron CT displacement experiments，and flow numerical simulation. The results show that the multi-scale pore sizes in low-permeability sandstones are featured by bimodal distribution.The movable fluids mainly occur in large pores（0.1 -10 μm），while the irreducible water mainly occurs in micropores（< 0.1 μm）. When the crude oil enters the low-permeability sandstone，it preferentially occurs in the large pores，and the sandstone with favorable physical properties shows a more significant differential occurrence of crude oil. For the sandstone with relatively favorable physical properties，the microscopic remaining oil mainly occurs in the large pores in the form of pore filling. For the sandstone with worse physical properties，the microscopic remaining oil mainly occurs in the micropores. The pore-filling remaining oil is formed by the weak sweep of relatively large pores due to the dominant flow channel generated by the heterogeneous pore structures during water flooding，which is the key target of potential tapping. By reducing the oil-water interfacial tension and increasing the displacement speed，the dominant flow channels can be effectively reduced，and the percentage of producing remaining oil in lowpermeability sandstones can be improved.