［Objective］To address the premature cracking and delamination of steel structurecoatings induced by vibration and thermal deformation in dynamic service environments，this studydeveloped a fast-curing aspartic acid-modified polyurethane topcoat with enhanced weather resistanceand dynamic fatigue resistance. The aim was to improve the long-term protection of steel structuresunder harsh conditions.［Methods］ The effects of key formulation components including the resin system（hydroxyacrylic-aspartic acid hybrid resin），curing agent，and pigment volume concentration（PVC）on coating performance were systematically investigated. The optimized coating was preparedand subjected to comprehensive evaluation through tensile tests，UV aging，thermal cycling，and combined vibration fatigue testing.［Results］At a hydroxyacrylic-to-aspartic acid resin mass ratio of 1∶1 and a PVC of 0.20，the coating demonstrated optimal performance：rapid curing（full drying achieved within 1 hour at 45 ℃）， excellent mechanical properties（tensile strength：7. 3 MPa； elongation at break：140%）， outstanding weather resistance（no chalking after 2 000 hours of UVB aging，with 54. 6% gloss loss）， and superior dynamic fatigue resistance（no cracking or delamination after 20 thermal cycles and 10 million vibration cycles）.［Conclusion］ The aspartic acid-modified polyurethane topcoat demonstrated rapid curing，excellent mechanical properties，high weather resistance，and dynamic fatigue resistance. This significantly extended the service life of steel structuressubjected to temperature fluctuations and vibrational stresses. This work provides a novel solution forthe long-term protection of dynamically serviced facilities.