Abstract: In order to investigate the cracking mechanism of cutout under compressive stress by live loads, the thermal elastic-plastic FEM model of orthotropic steel bridge deck was adopted and element birth and death was used to simulate the welding process of foorbeam, then the coupled thermal-mechanical simulation of the welding and weld condensation processes were realized, the welding thermal field and stress field of the foorbeam were obtained, as well as the residual stress distribution of cutout was acquired, Meanwhile, the fatigue life of the cutout was evaluated by the field fatigue test. The research shown that the variation of welding temperature along the cutout was significant, the residual tensile stress at the minimum net section of the cutout reached nearly 300 MPa. Coupling the compressive stress under the wheel loading, the fatigue cracking occured at the floorbeam cutout.