In the context of intertwined challenges of low fertility and gender equality, clarifying the intra-household fertility decision-making mechanisms is of great significance. Drawing on data from the 2018 and 2022 China Family Panel Studies (CFPS), this study adopts a couple-centered perspective and applies the Diagonal Reference Model to quantify the relative influence of husband's and wife's fertility preferences on actual fertility behavior, thereby uncovering the underlying gender power dynamics. The results indicate that family fertility behavior is highly contingent upon the consistency of both partners' intentions, with the concordance of spousal preferences exerting a significant impact on behavioral outcomes. In cases of discordance, the husband's fertility intention tends to predominate, reflecting his relatively dominant role in reproductive decision-making. Further analysis indicates that having a son, residing in an urban area, and a wife's higher educational attainment relative to her husband may enhance the wife's bargaining power to some extent, but they are insufficient to fundamentally alter the gender-based power structure deeply entrenched in patriarchal culture. This study contributes to a deeper understanding of family fertility decision-making mechanisms and offers insights for the formulation and optimization of fertility-supportive policies.