The study examined the relationship between family function and blood glucose management behavior in 245 patients with gestational diabetes mellitus. Research included three measurements during pregnancy: at 24–28 weeks, 32 weeks, and 36–42 weeks of gestation. Results showed that good family function at the first measurement significantly reduced pregnancy-related anxiety (β = −0.26) and increased hope (β = 0.18) and proper blood glucose management decisions (β = 0.24). Pregnancy-related anxiety decreased hope and proper decision-making, while hope positively influenced blood glucose management behavior. The analysis demonstrated that pregnancy-related anxiety and hope mediated the effect of family function on blood glucose management behavior. The authors recommend family-centered interventions, anxiety screening, and enhancing hope through psychological support and health education.