Based on the quantum chemistry ab initio ( QCAB) calculation method, density functional theory methods ultrasoft pseudopotential method and semi - empirical interatomic pair potential combined, the cohesive energy of mar-tensite crystal cell of the high-carbon alloy steel DM8A and DM8 was calculated. The analysis of the calculated results shows as follows. ( 1 )The cohesive energy of the construction with Si-C or Ni-C is stronger than the construction with C, so both Si and Ni can intensively strengthen the high-carbon alloy steel as solid solution. Furthermore, the value of the cohesive energy of crystal cell of the construction with Si-C is higher than that of the construction with Ni-C, the proportion of the element Si-C and Ni-C in the alloy directly influences on the martensitic strength and the mechanical characteristics of the alloy. (2) Because the atomic mass of Si is much less than that of the other alloyed elements, the proportion of the construction Si-C is very large when same quantity of the alloyed element was added to the alloy, and then the total cohesive energy of the alloy is big. When the quantity of Si was lessened in the alloy adding less Ni at the same time, the total cohesive energy of the alloy system is decreased and transformation process of microstructure is accelerated during tempering at low temperature.