Using sizing agents instead of various nanoparticles to modify carbon fibers is widely recognized as the most practical approach to address processing issues and improve interfacial properties in carbon fiber reinforced polymer composites. However, a limited understanding of sizing agent evolution during composite manufacturing hinders comprehensive theoretical guidance for sizing treatment, thereby limiting further enhancement of composite performance. Here we disentangled the sizing agents into chemical anchoring and physical adsorption components, and elucidated the sequential wetting, diffusion, and crosslinking evolution processes of sizing agents across scales. By manipulating the proportion of chemical anchoring and physical adsorption in the sizing agents, the interfacial modulus gradient and infiltration efficiency were synergistically optimized. Consequently, significant improvements of 26.2 % in interfacial shear strength (IFSS) and 52.9 % in transverse fiber bundle tensile (TFBT) strength were achieved, indicating enhanced interfacial stress transfer and reduced internal defects in the composites. In summary, this work revisited the cross-scale evolution and mechanism of sizing agents during composite manufacturing, and thus provided a new paradigm for optimizing composite performance.