Abstract: To address the critical challenge of weak multi-scale integration and difficulty in achieving multi-objective synergy in ultra-high performance concrete (UHPC), a novel multi-scale collaborative design framework was proposed with water/paste film thickness (t_WFT/ t_PFT) as key linking parameters. The framework was implemented at three scales: at the paste scale, equal-volume replacement of unhydrated cement with supplementary cementitious materials was conducted, binder gradation was optimized through discrete element simulation, and the water-to-binder ratio was determines based on t_WFT; at the mortar scale, aggregate gradation was optimized using the compressible packing model with optimal paste content determined by t_PFT; at the composite scale, the critical fiber dosage was determined based on packing characteristics and mechanical contribution. Results show that within the paste scale, the quaternary binder system (PB4-20) with a t_WFT of 20 nm achieves optimal performance in workability (245 mm spread), mechanical properties (28-day compressive strength of 103.2 MPa, flexural strength of 20.3 MPa), and microstructure (harmless pore proportion > 64%). Further optimization of aggregate gradation (MG1) and t_PFT (50 μm) reduced the paste content by 5.3% while increasing the 28-day compressive strength to 113.2 MPa, resulting in both material-saving and performance-enhancing effects. The optimal steel fiber volume fraction is 1.5%, with diminishing returns beyond this point. This framework establishes a quantitative methodology to holistically optimize the workability, mechanical properties, and resource efficiency of UHPC, guiding its transition to green, high-performance applications.