Abstract: To address the complex multiscale resin flow and the tendency for void formation during liquid molding of non-crimp fabrics (NCFs), this study develops a microfluidic constant-flow infusion platform and a fiber tow saturation evaluation method, enabling quantitative characterization of intra- and inter-tow flow behaviors and revealing distinct mechanisms of void formation within and between plies of 0°/90° biaxial fabrics. Within a single NCF layer, inter-tow flow readily exhibits fingering, which is impeded near stitching yarns, leading to air entrapment. Between layers, the multiaxial architecture of NCFs induces interlayer flow velocity differences, resulting in air retention in low-velocity layers. An in-plane waviness ratio is introduced to uniformly characterize the NCF structural features, and high-fidelity simulations are performed to analyze its effect on permeability. The discrepancy in permeability between simulations and experiments is less than 9%, validating the reliability of the numerical method. Numerical results show that the permeability of NCFs is positively correlated with the in-plane waviness ratio. As the waviness ratio increases from 0.014 to 0.024, the warp permeability increases from 2.91×10⁻¹¹ m² to 8.02×10⁻¹¹ m², while the weft permeability increases from 6.94×10⁻¹¹ m² to 9.49×10⁻¹¹ m². Analysis of the waviness ratio and porosity probability distribution indicates that fabrics with lower waviness ratios contain a higher fraction of small-scale pores, corresponding to a larger microscopic fluid filling volume. However, experimental analysis based on the microfluidic constant-flow infusion platform reveals a significant negative correlation between macroscopic permeability and multiscale impregnation uniformity. Therefore, in the design of liquid composite molding processes, relying solely on macroscopic permeability as an evaluation criterion is limited, and the influence of internal fabric structure on the actual filling process must also be considered.