Abstract: A medium carbon alloy steel was heat-treated by the liquid quenching and isothermal quenching with temperature process. The effects of austenitizing temperature and time, taking-out-of-liquid temperature and isothermal temperature and time on the microstructure and properties of the steel were discussed and the process was optimized. The results show that under the experimental condition, the ideal process parameters were as follows:Austenitizing temperature of 840℃ and holding time of 60 min, taking-out-of-liquid temperature of 238℃, isothermal temperature of 300℃ and isothermal time of 60 min. With this process, the matrix microstructure of the tested steel was composed of lower bainite and martensite, the hardness was 50 HRC, impact toughness was 26 J ·cm^-2 and abrasion loss was 18 mg.