Abstract: A group of co-modified phosphorus-containing waterborne polyurethanes(FOWPU) was synthesized by N'N-bis (2-hydroxymethyl) aminoethyl phosphonic acid dimethyl ester(Fyrol-6) and Exolit OP550 reacted with toluene diisocynate. The performance of the FOWPU was studied with limiting oxygen index (LOI), thermo-gravimetric analysis(TG), thermal gravimetric analysis with a Fourier transform infrared spectrometer (TG-IR) and differential scanning calorimetry(DSC). The results show that when the mass fraction of Fyrol-6 and OP550 is 15%, LOI of FOWPU15 is 30.4% and UL-94 achieve a V-0 classification.Compared with the unmodified waterborne polyurethane, the thermo-decomposition temperature of the FOWPU is reduced, but the amount of carbon residue is increased to 15.10%. Phase separation with increasing flame retardant content showes regular changes.