Abstract: In order to evaluate the corrosion resistance of the Zr alloy tube as used for the nuclear reactor fuel cladding in the pure water environment，the effects by different heat treatment processes on the microstructures and the corrosion resistance of the low Sn and low Nb Zr alloy tubes are studied. The matrix structure of the said alloy is characterized with the SEM and TEM. Moreover the corrosion test to the said alloy tube is also conducted in a hi-pressure autoclave under pure water condition at 360℃/18.6 MPa for so long as 300 days. The results reveal after annealed at 550℃ and hold for 5 h， the microstructure of the tube is completely re-crystallized，and its microstructure morphology is of uniform equiaxed grain structure；and its second phase is evenly distributed in the grains；however，the 茁 phase alloy tube as water quenched at 500℃ and for 5 h is not completely re-crystallized，and its microstructure features mainly lamellar shape. The corrosion resistances under the conditions of hi-temperature as 360℃ and high water pressure as 18.6 MPa are better than that of the commercial ZIRLO alloy.