Abstract: The effects of different heat treatment processes on the microstructure and properties of the HS05 steel as used for making the C110 casing are studied by means of performing different heat treatment processes for the said steel, and conducting mechanical property tests to and microstructure analysis of the specimen. The results show that under the same tempering conditions(700℃×100 min), the ideal microstructure properties can be obtained with different quenching processes (880℃ or 920℃). And under the same quenching conditions, keeping the merging and polygonization of the martensite phase lath structure can make the impact energy of the steel rising along with the increase of the tempering temperature.