The invention relates to hyperbranched poly-blend soft-segment modified chain extension anti-flaming waterborne polyurethane, which belongs to the field of flame retardant materials. The waterborne polyurethane is prepared by the following steps of after dehydrating macromolecule polyhydric alcohol, adding a hydrophilic chain extender and diisocyanate, reacting until -NCO content is constant, adding a phosphorus containing polyhydric alcohol macromolecule until -NCO content is constant, and adding a salt-forming agent A to obtain a prepolymer; adding water into the prepolymer, adding an acetone / butanone / N-methyl pyrrolidone solution of a phosphorus-containing diamine chain extender after adding water, and obtaining an emulsion; adding the emulsion into an AWHBPU water solution neutralized by a salt-forming agent B for emulsifying, spin-evaporating to remove a solvent, and obtaining the waterborne polyurethane. The waterborne polyurethane is subjected to soft-segment anti-flaming modification, so that a flame retardant property is improved, and the waterborne polyurethane is halogen-free and environmentally-friendly; through chain extension modification, a flame retardant property is improved, a mechanical property is improved, and the stability is improved; through blending the AWHBPU and the chain extension anti-flaming waterborne polyurethane, a mechanical property and the stability are further improved.