Objective To investigate the value of Tei index in evaluating the fetal cardiac function in gestational diabetes mellitus (GDM). Methods from January 2015 -2016 June in our hospital 47 cases of GDM in pregnant women with poor glycemic control (A group), 55 cases of GDM with good glycemic control in pregnant women (B group) and 70 cases of normal pregnant women (C group) as the research object, all pregnant women were singleton pregnancies. The left ventricular and right ventricular Tei index was measured by Doppler echocardiography at the time of delivery, 1-7d after delivery and 2-3 months after delivery. Results there were significant differences in left ventricular Tei index and right ventricular Tei index between the 3 groups (P < 0.05) after delivery, 1-7d after delivery and 2-3 months after delivery. Compare the same time between the two groups: A group fetal Tei index of left ventricular and right ventricular Tei index were significantly higher than that of B group, C group of fetus (P < 0.05), no statistical significance between the B group and C group of fetal left ventricular Tei index, Tei index difference (P < 0.05). Conclusion active and effective control of blood glucose can avoid the damage of cardiac function in GDM fetus. Poor glycemic control can damage the heart function of GDM fetal cardiac function, even within 2-3 months after the fetal abnormal level is still in.