Abstract: After different quenching and tempering treatments, the microstructure and properties of X80 steels plate with 52 mm thickness were studied by microstructure analysis and mechanical properties tests. The results show that after quenched at 890 ℃ and tempered at 660 ℃, quenched at 910 ℃ and tempered at 660 ℃ and multiple quenching and one time tempering heat treatment, the thickness central microstructure of X80 steels plate was all granular bainite(GB), yield strength and low temperature toughness of the steel all were improved. X80 steels had good low temperature toughness as quenched at 890 ℃. As quenching temperature was up to 910 ℃, austenite grain size was inhomogeneous, M/A strip appeared in large GB and low temperature toughness decreased. After multiple quenching and tempering heat treatment, austenite grain was fined, and M/A strip precipitated in particle way and distributed uniformly in GB structure, improved strength and toughness of the steel greatly.