A congenital diaphragmatic hernia (CDH) complicated with gastric perforation is extremely rare. Herein, we report an unusual case of unexpected intrauterine gastric perforation of a left side CDH with concurrent pleural effusion and ascites. A 21-year-old female underwent prenatal ultrasound at 37 weeks of gestation and revealed a left side CDH, pleural effusion with a large thick-walled cystic mass over the left thorax, ascites, and polyhydramnios. Under the impression of CDH with suspected gastric perforation, Cesarean delivery was arranged and a male neonate was delivered. The neonate received emergency laparotomy soon and a herniation originated from the foramen of Bochdalek and a perforation located in the stomach body along the greater curvature were found. The pathologic diagnosis was consistent with a spontaneous gastric perforation with ischemic change. Sonographic findings of pleural effusion and ascites associated with CDH are clues of antenatal gastrointestinal perforation.