Previous studies have shown that nuclear localization of METTL3 is associated with CDDP resistance. To identify key PTMS involved in the nuclear localization of METTL3 in CDDP-resistant ovarian cancer cells, we assessed the global methylation of arginine, as well as METTL3 phosphorylation, acetylation, O-GlcNAcylation, and crotonylation in CDDP-resistant and parental ovarian cancer cells. The results showed that arginine methylation of METTL3 was increased in CDDP-resistant cell lines. To further identify the arginine methylation sites that may be involved in the METTL3 resistance mechanism, we identified the methylation modification sites of METTL3 by mass spectrometry.