Abstract: Understanding how channel diversity affects consumers’ willingness to pay a premium for ecological agricultural products and through which mechanisms is important for improving the distribution system for these products. Drawing on social cognitive theory and risk communication theory, this study uses survey data from 1,500 consumers across 31 provinces in China and conducts empirical analyses using baseline regressions, moderating-effect models, a bootstrap parallel mediation model, and an instrumental-variable approach. The results show that: 1) Channel diversity significantly reduces consumers’ willingness to pay a premium. This finding remains robust after accounting for endogeneity and conducting a series of robustness checks, and the negative effect is stronger in regions with less-developed trust infrastructure. Channel heterogeneity analysis shows that the negative effect is stronger among consumers using online channels, particularly social e-commerce. Compared with consumers using only one channel, those using three or more channels have a significantly lower willingness to pay a premium. Subgroup analysis further indicates that this negative relationship is relatively stronger among older, higher-income, less-educated, and urban consumers, and is more pronounced for grains, coarse cereals, and legumes. 2) Greater reliance on brand trust in purchase decisions, stronger environmental awareness, and greater channel synergy mitigate the negative effect of channel diversity, whereas channel conflict reinforces it. 3) Information reliability partially mediates the relationship between channel diversity and willingness to pay a premium. The total indirect effect in the parallel mediation model accounts for 20.6% of the total effect, with the information verification and certification labeling pathways jointly accounting for 89.0% of the total indirect effect. These findings clarify the mechanisms and boundary conditions underlying the effect of channel diversity on consumers’ willingness to pay a premium for ecological agricultural products and provide empirical evidence for strengthening channel coordination and market trust systems.