The　supercritical　carbon　dioxide　(sCO2)　Brayton　cycle　has　been　the　focus　of　much　research　in　recent　years　because　of　its　high　efficiency　and　compactness.　One　of　the　key　issues　is　the　heat　rejection　of　about　half　heat　addition　to　the　sCO2　cycle,　which　needs　a　strong　and　reliable　cooling　system.　In　this　paper,　indirect　and　direct　cooling　systems　using　a　20-m　natural　draft　dry　cooling　tower　(NDDCT)　were　proposed　and　investigated.　One-dimensional　models　for　these　two　cooling　systems　were　selected　based　on　the　experimental　data　of　the　cooling　tower.　The　effects　of　the　ambient　temperature　on　the　heat　rejection　rate　and　sCO2　outlet　temperature　for　indirect　and　direct　cooling　systems　were　investigated,　respectively.　The　results　show　that　the　optimal　values　of　the　water　mass　flow　rate　can　be　found　in　the　indirect　cooling　system,　and　several　optimal　values　are　obtained　under　different　ambient　temperatures.　Under　the　same　operation　temperature,　the　overall　cooling　performance　of　the　direct　cooling　system　is　better　than　the　indirect　system,　especially　under　low　ambient　temperature　conditions.　Under　15　degrees　C　ambient　temperature,　the　exergy　efficiency　of　the　direct　cooling　system　is　greater　than　that　of　the　indirect　cooling　system　(＞200%).　The　results　of　this　work　illustrate　that　the　direct　cooling　system　is　more　appropriate　for　the　Gatton　cooling　tower　and　also　provide　some　references　for　the　dry　cooling　system　design　for　small-scale　sCO2　cycles　in　the　future.