For USIBOR 1500P boron steel, the austenitizing and quenching treatments of specimens were conducted at the die temperatures ranging from 25 ℃ to 450 ℃, and the microstructures and mechanical properties of the quenched specimens were researched. The results show that when the die temperatures are 25 ℃ and 450 ℃, respectively, Vickers hardnesses are 514 HV and 327 HV, respectively, and the relationship curve between Vickers hardness and die temperature was obtained. Compared with the specimen with the die temperature of 25 ℃,  the ultimate tensile strength of the specimen with the die temperature of 450 ℃ decreases by 34%, and the elongation after fracture increases by 20%. The area fraction of the quenched phases is identified and counted by scanning electron microscopy and a two-stage color etching, it is found that when the die temperatures are 25 ℃ and 100 ℃, respectively, the area fraction of martensite in the specimens remains high, and the area fraction of martensite reduces with the increase of the die temperature. When the quenching rate is reduced, there is more bainite formation,and the ferrite begins to form at the die temperature of 300 ℃.