Kommerell diverticulum (KD) is a rare cardiovascular malformation, which is usually diagnosed after birth. To our knowledge, there is no report of prenatal diagnosis of KD so far. Here we present a case of RAA, KD with ALSA prenatally. We confirmed the prenatal diagnosis with a new modified cardiovascular casting technique, which perfectly demonstrated the cardiovascular malformations of the fetus. Our case demonstrates that the modified cardiovascular casting technique can distinctly delineated correlations and spatial structure of heart and cardiac vessels, and this new approach of casting combined with clinical diagnosis may have a role in postnatal diagnosis and clinical teaching.