a new halogen-free phosphorus-nitrogen flame retardant (FR) was synthesized from triethylenetetramine, phosphorous acid, urea and other raw materials. Thermogravimetric(TG) analysis suggested that FR had good thermal stability, there was still 16.3% carbon residue at 800 °C. When the content of FR is 30%, the LOI of flame retardant composites (FR-PP) is improved from 18.0% to 25.4%, reaching the V-0 level of UL-94. SEM(Scanning electron microscope) and EDS (Energy dispersive spectrometer) results indicated that FR was successfully put on PP. The mechanical test showed that the tensile strength of FR-PP decreased from 20.8MPa to 13.1MPa, and the notched impact strength decreased from 34.5kJ/m2 to 31.6kJ/m2.