The Chang 8 ultra-low permeability reservoirs of Honghe Oilfield suffer from high water flooding pressure and low oil-displacement efficiency. Chemical flooding could be a method to enhance the oil recovery in Chang 8 ultra-low permeability reservoirs. However，the adaptability of flooding agents in reservoirs is not clear. Therefore，the interfacial activity，pressure reducing and oil displacement ability of three types flooding agents，including surfactant，nano emulsion，and a silica nanofluid， were comparatively studied and their adaptability in Chang 8 ultra-low permeability reservoirs was analyzed. The results showed that the pressure-reducing rates of the 0.3% surfactant AMS，0.5% nano emulsion LIE，and 0.3% the silica nanofluid were 15.1%， 5.8% and 9.1%，respectively，under single-phase seepage conditions. The surfactant exhibited the highest pressure-reducing rate， which resulted from its superior wettability alteration ability. The wettability of rock changed from intermediate-wet to weak oil-wet under the effect of the surfactant. In contrast，the surfactant could not achieve pressure-reducing under two-phase seepage conditions because the surfactant could not inhibit the formation of oil-in-water emulsions. Meanwhile，the nano emulsion LIE and the silica nanofluid ASN exhibited favorable pressure-reducing performance due to their interfacial tension reducing ability and oil-in-water emulsion inhibition ability. The nano emulsion exhibited the highest pressure-reducing rate，being of 38.6%，because the interfacial tension reducing ability of the nano emulsion was better than that of the silica nanofluid. In nature core flooding experiments，the surfactant，the nano emulsion，and the silica nanofluid achieved enhanced oil recovery of 26.67 percentage point， 23.51 percentage point and 16.35 percentage point，respectively. The surfactant exhibited the best enhanced oil recovery ability. However，considering that the surfactant could not achieve pressure-reducing effect under two-phase seepage conditions，the nano emulsion was the best alternative for chemical flooding in Chang 8 ultra-low permeability reservoirs.