The paper addresses the assessment of the high-temperature oxidation behavior of T91 in supercritical boilers. The trend to higher steam temperatures and longer periods of full-load operation greatly increases the oxidation corrosion on the steam-side surface. The oxide films can lead to major failures and consequently to reduced plant availability. The exfoliation of the oxide scale may block the tubes somewhere in the system with the potential for causing tube explosion. The oxide scale of T91 was sampled and analyzed by the energy dispersive X-ray spectrometry (EDXS) and the X-ray diffractmeter (XRD). The mechanism of oxidation corrosion and scale exfoliation, as well as its influence factor, were described. The measures were brought forward so as to provide a scientific guidance for dealing with oxidation corrosion and oxide exfoliation on a large scale in T91 in the supercritical boiler.