Abstract:The Potential-pH diagrams of the Zr-H2O system at temperatures of 298 K, 333 K, 373 K and 423 K were be established through extensive study of thermodynamic data and thermodynamic calculation coupled with experimental results? The Potential-pH diagram at 298 K concides with that at the same temperature drawn by Professor M.Pourbaix. Comparing and analyzing potential-pH diagrams of Zr-H2O system at different temperatures, it is evident that with the temperature increasing there is no great change of the immunity area of zirconium, but remarkable reduction of the passivation area, which theoretically accounts for the high temperature limitation of zirconium.