The harmless treatment of oily sludge in oilfield production is difficult and costly. Reinjection of oily sludge is a low-cost harmless treatment technology. The conventional reinjection profile control method can only reinject the oily sludge particles with smaller particle size，which can not fully recycle the oily sludge. Therefore，the oily sludge particles were ball milled to the micro-nano scale，and then petroleum sulfonate surfactant was added to form a stable oil displacement system by stirring， ultrasonication and centrifugation. The particle size distribution，emulsification ability and oil displacement performance of oily sludge flooding system with micro-nano particle were studied. The results showed that the median particle size of oily sludge micro-nano particle in oil displacement system was 158 nm. The system could maintain good suspension after standing at room temperature（25 ℃）for 4 days. The time of complete separation of oil and water was equal or greater than 5 min. The interfacial tension between the system with kerosene at 60 ℃ was 7.4×10^-3 mN/m，indicating strong emulsification ability. Due to the dual effects of emulsification and plugging，the oily sludge micro-nano particle flooding system had better injection capacity and oil displacement effect than surfactant flooding，which was suitable for medium and low permeability reservoirs. Under the condition of 60 ℃，injection volume of 0.5 PV and injection rate of 1 mL/min，the oil displacement efficiency was about 20 percentage points higher than that of water flooding and about 8 percentage points higher than that of surfactant flooding. The preparation method of oily sludge micro-nano particle flooding system could completely treat oily sludge，and then realize the efficient reuse of oily sludge.