The thermal stress-induced multiple fracture of the Fe-Zn intermetallic compound coating layer of galvannealed steel was investigated for samples with IF (interstitial free steel) and SPCC (steel plate cold commercial, Japanese Industrial Standard) as substrates. The analysis of the measured length of the multiply fractured coating layer showed that the fracture strength of the coating layer was 260-280 MPa and the residual stress around 720-740 MPa of the coating layer was reduced to around 130-140 MPa through the multiple fracture. The influences of the coating layer thickness and the stress-strain curve of the substrate on the multiple fracture behavior of the coating layer were also clarified.