Based on a combination of Monte Carlo models of fast electrons and species(N₂⁺,N⁺,N_r),Creation rates of atomic species(N⁺,N)and energy,density and angular distribution of species(N⁺,N_f)bombarding negative target in nitrogen dc discharge plasma-assisted nitriding of steel surface are investigated for e^-+N_2s→N⁺+N_s+2e^-及N₂¹+N_2s→N⁺+N_s+N₂.It is found that these is an optimum discharge temperature for the energy distribution of species(N⁺,N_f)at the cathode,creation rate and density of atomic species(N⁺,N)decreases with increasing temperature at steel surface,calculated results are generally in agreement with experimental ones.