Abstract: Based on the impact load-displacement curves recorded by instrumented impact tests, the energy distribution characteristics of low-alloy high-strength steels containing Nb, Ni and Ti in the instant of impact fracture at -70℃ were quantitatively analyzed. The results show that:The impact absorbed energy could be divided into two parts of crack arrest energy and crack propagation energy; the holding time of normalization process at 910℃ had little influence on the crack arrest energy of the low-alloy high-strength steels, and had remarkable influence on the crack propagation energy. In addition, the microstructure of the low-alloy high-strength steels was analyzed to ascertain the strength mechanism and toughness mechanism of low-alloy high-strength steels.