Mo/Al2O3 solar energy selective absorbing coating is simulated on computer. Mo/Al2O3 metal ceramic mixed-film is deposited on stainless steel sheet using magnetron sputtering. Maxwell-Garnett effective medium theory is applied to analyze the optical constant of Mo/Al2O3 granular film. As the wavelength λ changes, the variation regulation of Mo filling factor and the optical constant n, k of metal ceramics granular film at 300 nm~800 nm is theoretically calculated, which is based on Mo/Al2O3 bulk materials and optical constant of sputtering film. The coating is simulated successfully with Al2O3 optical parameter found in references. The thickness of each film layer and the proportion between Mo and Al2O3 are simulated completely, thus the function of each layer is defined and the optimal thickness of film and Mo/Al2O3 proportion are determined. Production technology is improved.