Paint aging will take a long time under the conditions of natural exposure,their failure mechanism cant be known quickly.So the artificial UV-condensation accelerated aging test is used to alkyd system and polyurethane system,and the coating aging was analyzed by using SEM,gloss meter and FTIR.The results shown that their failure mechanism is different,the main reason that life of alkyd system was lower than polyurethane system is its weak water-resistant.If the water-resistant of alkyd system can be improved,the use area of alkyd system will be expanded.