Abstract: White oil is used as a pore-forming agent in the production of wet polyethylene (PE) separator for lithium ion battery. In order to explore yellow appearance and yellow substances in white oil recycling processes, Fourier transform infrared spectroscopy was employed to investigate the relationship between structural changes and yellowing resistance of white oil, PE, and antioxidant 1010 (I1010) under simulated production conditions. Additionally, the relationship between structure change, yellowing resistance and the ratio of white oil, PE and I1010 mixtures were studied. Furthermore, the yellow substance in recovered oil was qualitatively analyzed using high performance liquid chromatography and high resolution mass spectrometry. The results show that oxidation of white oil, PE, and I1010 occurred in the PE separator production process, and the production of the yellow substance is the results of the synergistic action, in which PE and I1010 are the main factors. The yellow substances were identified as aromatic esters and I1010. This research provides valuable insights for improving white oil recycling technology.