The　traditional　Structural　SIMilarity　(SSIM)　index　has　higher　computation　complexity　compared　with　Peak-Signal-To-Noise-Ratio　(PSNR).　In　order　to　solve　this　problem,　we　propose　a　two-stage　optimization　algorithm　to　reduce　the　computation　complexity　of　SSIM.　First,　floating-point　operations　in　the　calculation　process　of　SSIM　are　converted　to　fixed-point　ones.　Then,　the　repeated　calculation　rule　of　the　iteration　operation　in　SSIM　is　analyzed　and　the　repeated　operations　are　subsequently　removed　via　modifying　SSIM　calculation　method.　Experiment　results　show　that,　in　comparison　with　the　original　SSIM　algorithm,　the　proposed　algorithm　obtains　24.12%　of　computation　time　reduction　with　negligible　accuracy　decrease.　©　Published　under　licence　by　IOP　Publishing　Ltd.