The waterborne polyurethane coatings modified by linseed oil were prepared in a method of ammonolysis. The influence of reaction time and temperature of the linseed oil ammonolysis on structure and properties of the waterborne polyurethane coatings was investigated and discussed. It has been shown in this work that the preferred ammonolysis temperature would be 102~118°C, the reaction time could be about 80 min, and structure of the modified waterborne polyurethane was analysed by FTIR. The touch-dry time of the modified waterborne polyurethane with drier would be shorter than that of non-modified waterborne polyurethane, normally in a week, and the stability of the modified waterborne polyurethane coating in water could stand for 3 months under room temperature. The TGA results of the coatings showed that the weight loss started at about 294°C.