Abstract: Zirconium hydride, as a moderator of the space reactor, working at temperature over 650 ℃, in which the initial H/Zr atomicity ratio (H/Zr) is about 1.85, will face a risk of hydrogen release and yield reduction of the moderation. Therefore, it’s necessary to find a prevention method. ZrO₂ is a potential material to prevent the hydrogen release. The verification of the prevention method was realized by the hydrogen release test and the XRD method which could minimize the variation of the H/Zr. The result indicates that both the plain sample and the pre-oxidized one lose a tremendous amount of hydrogen when they are placed in He atmosphere at 650 ℃ for 120 h, furthermore, a new substance Zr₃O comes into being on the surface of the latter. However, when it is in the gas mixture of He and CO₂, the hydrogen release of the pre-oxidized sample is negligible. A conclusion can be draw that the CO₂ sustains the ZrO₂ structure and the method is available.