This　paper　investigated　the　effects　of　nano-CaCO3　(NC)　with　different　contents　(i.e.,　0-4%　by　mass　of　cement)　on　hydration,　micro-structure　and　mechanical　properties　of　ultra-high　performance　engineered　cementitious　composites　(UHP-ECC)　and　clarified　the　inherent　relations　of　multi-scale　performances　of　UHP-ECC.　At　the　micro-scale,　the　heat　evolution　analysis　was　firstly　conducted　and　the　results　showed　that　NC　accelerated　the　heat　of　hydration　of　UHP-ECC　matrices　due　to　its　nucleation　and　dilution　effect.　Then,　the　phase　developments　of　NC　modified　UHP-ECC　matrices　were　discussed　using　the　thermal　gravimetric　analysis/differential　thermal　gravimetric　analysis,　which　proved　the　filler　effect　of　NC.　Mercury　intrusion　tests　(MIP)　indicated　that　not　only　the　porosity　but　also　the　critical　pore　size　decreased　with　the　increase　of　NC　content　up　to　3%,　beyond　which　the　porosity　increased　due　to　the　agglomerate　of　NC.　Finally,　the　morphologies　of　ultra-high　molecular　weight　polyethylene　fiber　surfaces　and　fiber-matrix　interfaces　were　observed　by　scanning　electron　microscope.　At　the　meso-scale,　single　fiber　pullout　tests　were　conducted　and　verified　that　the　frictional　stress　between　fiber　and　matrix　reached　the　maximum　value　with　NC　content　of　3%,　which　was　in　accordance　with　the　results　of　MIP　tests.　At　the　macro-scale,　the　optimal　NC　dosage　to　enhance　the　compressive,　tensile　and　flexural　properties　of　UHP-ECC　was　found　to　be　3%,　which　was　strongly　supported　by　the　results　obtained　at　micro-　and　meso-scale.　Hence,　intense　linkages　between　the　micro-,　meso-　and　macro-scale　performances　of　UHP-ECC　were　exhibited,　and　the　micro-　and　meso-scale　properties　induced　a　decisive　impact　on　the　mechanical　properties　of　UHP-ECC　at　composites　level.　(C)　2019　Elsevier　Ltd.　All　rights　reserved.