High-efficiency,　large-area,　non-destructive,　and　high-precision　polishing　of　alumina　ceramics　was　achieved　by　picosecond　laser　in　an　overlapping　parallel　line　scanning　mode.　The　ablation　law　and　the　ablation　threshold　during　polishing　were　determined.　The　surface　roughness　(SRa)　after　polishing　was　decreased　by　82%　compared　with　that　of　the　unpolished　sample　(1.80　mu　m)　and　the　minimum　SRa　achieved　was　0.32　mu　m,　when　the　laser　energy　density　was　5.09　J/cm(2),　scan　rate　was　800　mm/s,　and　scanning　path　gap　was　10　mu　m.　The　polishing　efficiency,　which　was　described　by　the　processing　area　per　second,　was　55　mm(2)/s.　The　mechanism　of　picosecond　laser　polishing　was　not　direct　removal　of　surface　material,　but　entailed　the　recrystallization　of　nanoparticles　excited　by　the　ultrafast　laser.　The　excited　nanoparticles　melted　and　recrystallized　to　form　a　layer　of　dense　fine　crystal　structure　on　the　ceramic　surface,　which　resulted　in　the　decreased　SRa.