The　effect　of　the　volume　fraction　of　nickel　on　the　optical　properties　of　Ni-Al2O3　solar　selective　absorbing　films　was　investigated　by　computer　simulation.　The　knowledge　obtained　was　used　to　guide　the　optimization　of　Ni-Al2O3　coatings　fabricated　by　aqueous　sol-gel　method.　The　results　of　theoretical　simulation　showed　that　the　double　absorbing　coatings,　of　which　consists　of　a　base　layer　with　metal-like　character　and　a　middle　layer　with　volume　fraction　less　than　0.5　times　of　the　base　layer,　together　with　an　anti-reflection　top　layer　could　produce　excellent　optical　absorption.　Based　on　the　principles,　the　optimized　Ni-Al2O3　coatings　were　fabricated　by　aqueous　sol-gel　method,　which　attained　a　high　solar　absorptance　of　0.94　and　a　low　thermal　emittance　of　0.04.