The invention provides an environment-friendly polyurethane flame-retardant coating which is prepared from the following raw materials in parts by mole: 100 parts of diisocyanate, 6-40 parts of polyhydric alcohol, 10-35 parts of hydrophilic compound, 5-35 parts of a flame retardant and 9-37 parts of a chain extender. The flame retardant is a compound shown in a formula (I), wherein, R is selected from H, hydroxymethyl or alkyl containing 1-10 carbon atoms. The polyurethane flame-retardant coating provided by the invention is a degradable coating and has a good film forming effect, can be stored at room temperature for more than one year, is low in cost and has a wide market prospect.