Surface　atomic　structure　is　closely　related　to　the　physical　and　chemical　properties　of　materials.　Although　cupric　oxide　(CuO)　surfaces　have　been　widely　reported,　to　the　best　of　our　knowledge,　the　low　Miller　index　and　easily　exposed　CuO(001)　surface　has　not　been　yet　investigated　in　experiments　at　the　atomic　scale.　Herein,　for　the　first　time,　we　report　the　atomic　structures　of　CuO(001)　surface　combining　aberration-corrected　scanning　transmission　electron　microscopy　and　first-principles　calculations.　Interestingly,　akin　to　the　(1　1　1)　surfaces　of　FeO,　CoO　and　NiO,　a　unusual　tetrahedral　reconstructed　structure　was　revealed　for　the　CuO(001)　surface.　The　low　energy　barrier　from　square-planar　to　tetrahedral　coordination　for　the　surface　CuO　4　unit　was　found　by　the　climbing-image　nudged-elastic　band　method.