Objective: To explore the effect of nutritional intervention based on behavioral change theory on healthy dietary behavior, blood glucose and pregnancy outcome of patients with gestational diabetes mellitus (GDM). Methods: A total of 104 patients with GDM admitted to The People’s Hospital of Bozhou from November 2018 to March 2021 were selected as the research objects and according to random number table method randomly divided into control group and observation group, with 52 cases in each group. The control group was given routine nutritional intervention, and the observation group was given nutritional intervention based on behavioral change theory. The dietary pattern, healthy eating behavior score, blood glucose [fasting plasma glucose (FPG), 2 hours postprandial blood glucose (2hPG), glycosylated hemoglobin (HbA1c)] and pregnancy outcome were compared between the two groups before and after intervention. Results: After intervention, the proportion of reasonable intake of protein (80.77% vs 59.62%), fat (73.08% vs 42.31%), carbohydrate (69.23% vs 42.31%) and healthy eating behavior score [(7.02±1.01) points vs (5.51±0.98) points] in the observation group were significantly higher than those in the control group (P<0.05). After intervention, the levels of FPG [(4.92±0.59) mmol/L vs (5.17±0.61) mmol/L], 2hPG [(5.52±0.54) mmol/L vs (5.89±0.58) mmol/L] and HbA1c [(5.15±0.37)% vs (5.42±0.48)%] in the observation group were significantly lower than those in the control group (P<0.05). The incidences of premature rupture of membrane (15.38% vs 38.46%), cesarean section (13.46% vs 48.08%), hypertensive disorders complicatin pregnancy (7.69% vs 23.08%) and macrosomia (1.92% vs 23.08%) in the observation group were significantly lower than those in the control group (P<0.05). Conclusion: Nutritional intervention based on behavioral change theory can effectively optimize the dietary pattern of GDM patients, strengthen healthy dietary behavior, thereby reducing blood glucose and improving pregnancy outcomes.