The invention discloses a preparation method for waterborne 
polyurethane with improved 
fire resistance by virtue of nano materials. Under the condition that a 
dibutyltin dilaurate catalyst exists, PTMG and IPDI (
isophorone diisocyanate) are mixed for reaction at the temperature of 75-95 DEG C for 1.5-3.5 hours, so that 
polyurethane prepolymer can be obtained; a hydrophilic chain 
extender, of which the weight of carboxyl groups is 1.2-3.2 % of that of the 
polyurethane prepolymer, and an 
acetone solvent, of which the weight is 12-25% of that of the polyurethane 
prepolymer, are added into the polyurethane prepolymer for reaction at 65-85 DEG C for 1.5-3.5 hours, then, 
triethylamine is added for 
neutralization reaction for 30-50 minutes, and water is added for emulsification, so that polyurethane 
emulsion A can be formed; nano material 
emulsion, with the weight being 5-10% of that of the polyurethane 
emulsion A, is added into the polyurethane emulsion A, and the mixture of the nano material emulsion and the polyurethane emulsion A is subject to shear agitation for 20-50 minutes under the condition that the pH value is 7, as a result, the 
fire resistance waterborne polyurethane can be obtained. The prepared 
fire resistance polyurethane is environment-friendly and low is price, and can meet the low cost requirement on fire resistance leather products by the market.