Aiming at the peaks overlapping in the field of X-ray diffraction, a new method for peaks separation was developed, and the parameters and recovery behaviors of crystal lattice of 30CrMnSiNi2A were investigated using RU-200V X-ray powder diffractmeter, by which the relationship between lattice parameters and carbon content at different tempering temperatures was obtained. Results show that the variation of lattice parameters of 30CrMnSiNi2A is consistent with high-carbon martensite on the whole, however there are some differences in the rate of change. The lattice parameter a is independent of carbon content, and slightly decreases with the rise of tempering temperature, while the amplitude of change for the lattice parameter c and carbon content is large, and a steep drop is observed in the process of quenching to the tempering temperature at 180 ℃, while the amplitude becomes flat aferwards for a higher tempering temperature.