Abstract: This paper aims to synchronously explore the fatigue damage evolution process in meso- and maroscales by experimental studying on a welded truss structural specimen as the scaled model of the longitudinal stiffening truss in long-span bridges. Several testing techniques are used to measure and analyze the damage evolution process so that mechanical properties and characteristic response are respectively compared in different scales. While hot-spot dynamic strains and extension of a plastic zone on the toe of the weld of the tested specimen are recorded by strain measurement technique, the fatigue cracking process is measured by optical technique and the variation of structural dynamic parameters due to the fatigue cracking is finally measured and identified according to dynamic testing technique. The results show that the fatigue damage evolution in meso-scale has few influences on the variation of mechanical properties in maro-scale, but the long-time evolution of damage accumulations in a local structure will certainly lead to the deterioration and failure of a global structure.