Through an experimental system to simulate the erosion of sandstorm environment and an aging test chamber to simulate the natural environment, an aging test of high and low temperature cycling was carried out specifically for the polyurethane coatings of steel structure. Then, a sandstorm washout test was completed for the non aging coating and that with varied aging degrees of steel structure. In addition, regarding the non aging coating and the coating with varied aging degrees of steel structure, scanning electron microscope(SEM), X ray energy spectrum(EDS) and X ray diffraction(XRD) were conducted to analyze the difference in coating elements and main crystal phases between the non aging coating and the coating with varied aging degrees. The results indicate that obvious crack, peeling and chap are observed on the aging coating of steel structure which has undergone temperature cycle, and that white crystal may appear as well. For non aging coatings of steel structures, the maximum washout rate appears at the angle of approximately 38°, while the value is between 38° and 45° for aging coating of steel structure. The sandstorm washout resistance capacity of the aging coating becomes lower, with the SEM definition of the coating dramatically declined after sandstorm washout. It has also been shown that significant changes in coating elements occur in the aging coating, while main crystal phases of the coating include CaMg(CO3)2, CaCO3, BaSO4 and TiO2. No new phase is generated during the aging process.