Ultra-high　performance　concrete　(UHPC)　delivers　outstanding　strength　and　durability,　yet　suffers　from　excessive　shrinkage,　high　cement　consumption,　and　environmental　impact.　To　address　these　limitations,　this　study　proposes　a　sustainable　and　performance-guaranteed　solution　by　incorporating　recycled　concrete　powder　(RCP)　as　a　partial　cement　replacement　to　produce　low-shrinkage　and　eco-efficient　UHPC.　A　key　innovation　is　the　development　of　a　constrained　dense　suspension　packing　(DSP)　theory,　which　goes　beyond　traditional　physical　packing　by　optimizing　the　synergistic　interaction　among　RCP,　silica　fume　(SF),　and　sand　gradation　to　tailor　both　workability　and　hydration　behavior.　This　design　approach　enhanced　flowability　by　108　%　and　improved　compressive　strength　by　up　to　87.3　%　at　30　%　RCP　content,　while　maintaining　performance　losses　within　acceptable　limits,　no　more　than　22.1　%　reduction　in　flowability　and　16.6　%　in　strength,　thereby　satisfying　the　requirements　of　GB/T　31387-2015.　It　was　also　found　that　across　the　full　RCP　replacement　range　of　10-50　%,　autogenous　and　chemical　shrinkage　progressively　decreased　with　increasing　dosage,　reaching　maximum　reductions　of　58.2　%　and　68.1　%　at　50　%　replacement,　primarily　due　to　the　dilution　effect　and　internal　curing　capability　of　RCP.　Microstructural　analysis　confirmed　that　higher　RCP　levels　suppressed　hydration　and　increased　porosity,　yet　delayed　internal　humidity　loss　and　stabilized　shrinkage　development.　Importantly,　a　life　cycle　assessment　(LCA)　verified　that　the　proposed　RCP-UHPC　substantially　reduces　energy　consumption　and　environmental　impact.　This　study　establishes　a　practical　and　applicable　approach　for　integrating　relatively　inert　recycled　construction　and　demolition　waste　powders　into　UHPC,　ensuring　dimensional　stability　and　structural　performance　while　improving　the　environmental　friendliness.