Compare the density neutrality of Neutral Density (ND) filter coated with different coating process when the coating material is Ni80-Cr20. The density neutrality value is 3.7% when the filter coated with magnetron sputtering technical, and the value is better than that of coated with Electronic Beam(EB) evaporation or resistance evaporation process, which valued 15%. Based on phase equilibrium theory, the reason why neutrality was reduced when coating Ni-Cr alloy under EB and resistance coatings were simulated and analyzed. At first of evaporation process, Cr is 2.8 times more than Ni, which causes density neutrality reduced. To certificate the analyzed results, Ni and Cr determination in both magnetron sputtering coating and resistance evaporation process were tested by Zeiss SEM and Oxford EDS. The experimental data is similar to theoretical results.