To explore the application of ultrasonic velocity vector imaging in cardiac function of fetuses with autoimmune diseases during pregnancy, in this study, 130 pregnant women and 130 healthy pregnant women eligible for prenatal ultrasound diagnosis in XX hospital in August 2016 and September 2018 were selected as the subjects. They were divided into experimental group and the control group, echocardiography and image collection were conducted in the two groups, and repeated experiments were conducted to exclude the occasionality. The results showed that in the comparison and analysis of basic information between the two groups of subjects, no significant differences were found between the two groups in terms of age, gestational age, weight and other indicators (P > 0.05), so there was no statistical significance in the basic information of the two groups of pregnant women. In the comparison and analysis of the differences between the two groups of subjects when the longitudinal contraction of the fetal left ventricle reached the peak velocity, 50% peak velocity and 75% peak velocity in each stage, it was found that the times when the contraction the basal segment, middle segment and the apex segment of lateral wall, posterior wall, and anterior wall of fetal heart reached the peak velocity, 50% peak velocity and 75% peak velocity were longer than that of the control group, and there were significant differences (P < 0.05). However, the times taken for the contraction to reach the peak velocity, 50% peak velocity and 75% peak velocity of the pre- and post-interval of the fetal heart in the experimental group were not significantly different from the control group (P > 0.05). For the inferior wall, there was no significant difference between the two groups in the time it took to reach the peak velocity in the basal segment and the middle segment (P > 0.05), but the peak value in the apex segment was statistically significant, and the time it took to reach the 50% peak velocity and the 75% peak velocity was statistically significant (P < 0.05). Ultrasonic velocity vector imaging (VVI) measurements of the left ventricular side wall and the left ventricular septum of the fetus in the two groups were analyzed. In the comparison of systolic peak velocity (Vs) and diastolic peak strain rate (SRd) between the two groups, it was found that VVI values of left ventricular lateral wall and left ventricular septum in the experimental group were smaller than those in the control group, with significant difference (P < 0.05). In the comparison of peak diastolic velocity (Vd), peak systolic strain rate at each stage (S), and peak systolic strain rate (SRs) between the two groups, it was found that VVI values of the left ventricular lateral wall and the left ventricular septum of the experimental group were lower than those of the control group, and both values were negative, with significant difference (P < 0.05). In the analysis of the relationship between Vs, Vd, and the gestational age of pregnant women in the experimental group, it was found that the relationship between Vs, Vd, and the gestational age of pregnant women in the experimental group was positively correlated, with a good correlation and statistical significance. To sum up, in the evaluation and analysis of fetal heart function of autoimmune diseases during pregnancy by ultrasound velocity vector imaging technology, it was found that pregnant women with autoimmune diseases during pregnancy would have an impact on fetal heart, but in general, it was significantly correlated with the increase of gestational weeks. Therefore, the results of this study can provide experimental reference for the clinical treatment of pregnant women.