The treatment of oily wastewater produced from polymer flooding (OWPF) is a big problem for offshore oilfields. A non-ionic surfactant named poloxyproylenated-poloxyethyleneated hydrogenated tallow alkyl secondary amine (PPHTA) was prepared. The relationship between its interfacial tension and temperature and the result of conductivity measurement showed that its phase inversion temperature (PIT) was about 60 degrees C and it had good interfacial activity. Then, OWPF was treated by PPHTA. It was interesting that the PPHTA had a good performance for treatment of OWPF at the temperature which was higher than its PIT. At 63 degrees C, after the treatment by PPHTA at dosage of 800 mg/L, the oil content in OWPF changed from 4724 mg/L to 72 mg/L. The reason was discussed and it was proposed that the PPHTA can displace the natural active agents in OWPF and form a new oil-PPHTA-water emulsion. When the temperature increased, the hydrophilic- lipophilic deviation (HLD) of oil-PPHTA-water moved to zero and the emulsion stability decreased. At the PIT, the most unstable emulsion was formed and it was destroyed after stirring. In addition, it is important to note that the floc of PPHTA was composed of oil drops and was not viscous. The result was different from the viscous floc caused by the cationic polymer.