Abstract: In the process of deep coal resource mining, the coal seam floor is subjected to significant water pressure, and the water hazard risk from the underlying aquifer is particularly prominent. The composite strata between the coal seam and the main water-threatening aquifer are characterized by highly complex structures, significant spatial heterogeneity in thickness, and substantial differences in water-bearing properties among different lithological sections. Therefore, the quantitative evaluation of their overall water-barrier performance has become a key link and core scientific issue for the proactive and precise prevention and control of coal seam floor water hazards. Traditional evaluation methods mainly focus on macroscopic geological characteristics and are unable to fully characterize the water-controlling effect of the internal microstructure of rock strata. Therefore, a more refined and comprehensive evaluation system is urgently needed. In this study, macro–micro dual-scale indicators were integrated. Fault complexity, effective aquiclude thickness, mass ratio coefficient, composite compressive strength, plastic-to-brittle rock thickness ratio, and core recovery rate were selected as macroscopic indicators, while composite area porosity and composite pore volume ratio were selected as microscopic indicators, thereby constructing a comprehensive evaluation index system. Based on the subjective and objective weights obtained by integrating the G1 method and the Criteria Importance Through Intercriteria Correlation （CRITIC） method using game theory, the constructed normal cloud model was applied to quantitatively evaluate the water-barrier capacity of composite strata. Meanwhile, the water-barrier performance of the mining area was compared and analyzed under the macroscopic single-scale framework and the macro–micro dual-scale framework. The results show that fault complexity and pore-structure parameters account for significant proportions in the index system, confirming that fault structures and the degree of microfracture development are the dominant factors controlling the water-barrier performance of such composite strata. The comprehensive evaluation based on the normal cloud model indicates that the overall water-barrier capacity of the floor composite strata in the study area is relatively weak. Compared with the traditional single macroscopic-scale evaluation, the dual-scale evaluation incorporating microscopic indicators can more accurately capture the water-controlling effect of internal microstructural defects in rock strata, and the evaluation results are highly consistent with the known fault distribution and actual mining conditions of working faces. By introducing microscopic indicators, namely composite area porosity and composite pore volume ratio, a macro–micro dual-scale evaluation index system based on multi-factor integration was established. The reliability of the proposed model and evaluation results was further verified through comparison with known fault distribution and working-face mining conditions. The research results not only deepen the understanding of the water-barrier mechanism of complex rock strata, but also provide a quantitative evaluation tool for mine water hazard prevention and control under similar geological conditions.