Using diphenyl chlorophosphate and lignin as raw material, lignin-based charring agent with phosphorus (Lig-P) was synthesized by one-step method, and a series of intumescent flame retardant polypropylene with Lig-P, ammonium polyphosphate and pentaerythritol were prepared by double roller mixer. FT-IR, XPS and TGA were used to characterize the structure and thermal degradation property of Lig-P, and the analysis results suggest that the initial degradation temperature of Lig-P rises from 214 ℃ to 226 ℃, and its residue at 500 ℃ increases from 2% to 35% in air atmosphere, showing that Lig-P has good thermal stability and charring ability. Cone calorimeter test results confirm the significant decrease of peak heat release rate and total heat release of Lig-P-IFR/PP. Furthermore, the analysis results of residual char after cone calorimeter test by digital photograph, SEM and LRS reveal that Lig-P-IFR/PP forms continuous char layer with higher graphitization degree. Moreover, the LOI of Lig-P-IFR/PP reaches 31% as well as its passing UL-94 V-0 rating, and its tensile strength is significantly higher than that of Lig-IFR/PP, and reaches 22.5 MPa.