Polyurethane is a general term for a class of macromolecule compounds with a carbamate structure in the molecular structure, usually made of polyisocyanate and polyol by polyaddition reaction. In view of the diversity of isocyanates and polyols, the resulting polyurethane can be from soft to hard, from brittle to tough, from high elasticity to a certain form of rigid product. Polyurethane coatings also have a wide range of performance adjustments. According to the type of isocyanate used in the preparation of polyurethane, polyurethane emulsion and the corresponding paint can be divided into two kinds of aliphatic and aromatic. Aliphatic film has excellent weather resistance and anti-yellowing, can be used as outdoor decorative paint; aromatic water-based polyurethane used to make interior decoration paint. The polyols used are polyether polyols, polyester polyols, polyolefin polyols, etc., resulting in polyether polyurethane water-based paint, polyester polyurethane water-based paint and other titles.