Abstract: Using depolymerized lignin(DL) as raw material, Schiff base nitrogen-containing lignin(N-DL) was prepared by phase transfer ultrasonic method, and then further reacted with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO) to synthesize nitrogen-phosphorus modified DL(NP-DL). NP-DL was a new type of expanded lignin-based nitrogen and phosphorus flame retardant. The structure and performance of NP-DL were characterized by FT-IR, ¹H NMR, ³¹P NMR, TG, TG/FT-IR, TG/MS, GPC and XPS. The results showed that N and P were successfully introduced into the depolymerized lignin; TG analysis showed that the carbon residue rates of NP-DL at 600 and 800℃ were increased by 1 285.5% and 362.6% compared with those of DL, respectively. The test results of TG/FT-IR and TG/MS showed that NP-DL was thermally degraded to produce phosphorus: OP⁺ with m/z=47, H₃PO with m/z=50, O₂P⁺ with m/z=63 andHO₂P⁺ with m/z=64 proved that the phosphorus-containing compounds produced during the pyrolysis of NP-DL inhibited combustion.