Abstract: By using the internal heating method, reactor stimulation loop corrosion experiments were carried out in the solution containing 650 mg/L boron and 3.5 mg/L lithium, at the temperature of 346.7 ℃ and pressure of 15.5 MPa, to study the properties of domestic ZIRLO. The optical microscope, transmission electron microscope and pulse heating inert gas fusion infrared absorption method were selected to characterize the ZILRO samples corroded for 2, 18, 250 d. The results show that the main types of the grains of oxide film formed on domestic ZILRO are columnar grains and equiaxed grains. As the corrosion time increasing, the columnar grains located at the outer part of the oxide film gradually transform into equiaxed grains, which will lead to the increase of the grain boundary density and oxygen diffusion channels. The main types of second phase particles are containing Nb particles and containing Fe and Nb particles respectively, with the shape of ellipsoid. The corrosion process does not change the structure and content of the second phase particles, and most of the particles embed in oxide films remained un-oxidized state. With the increase of corrosion time, the number and the size of the pores and microcracks in the oxide film also increase, and most of these cracks are located at the wave peak of the O/M interface or the second phase particles due to the tensile stress effects. As for the hydrides generated from the corrosion reaction, the content of these hydrides increases from 10 ppm to 80 ppm, and the size increases from tens of microns to hundreds of microns, which are mainly distributed circumferentially.