Recently, research reports on application of CFRP plates to repair of fatigue cracks initiated in steel structures are published. CFRP plates are often separated from steel plates, due to high shear stress produced in the adhesive at the end of CFRP plates and at the edge of fatigue cracks. The debonding behavior of CFRP plates from the steel plate which is divided into two by a fatigue crack can be given by that for butted steel plates. In this research, the debonding behavior of CFRP plates adhered to butted steel plates is theoretically investigated. Then, the debonding behavior is also analyzed for the case that a fiber sheet is inserted between steel and CFRP plates.