Objective To investigate the clinical value of locating the interspinous space by ultrasound imaging technique for combined spinal and epidural anesthesia of cesarean section. Methods Two hundred and forty pregnant women who were going to undergo the cesarean section were randomly divided into the control group (traditional landmark locating method, n=120) and ultrasound group (ultrasound imaging technique locating method, n=120). The space between the third and fourth lumbar vertebrae was properly located and combined spinal and epidural anesthesia was performed. Before the surgery, the anesthesia effect was evaluated for recording height, body mass, body mass index, time for locating before anesthesia, the number of punctures for combined spinal and epidural anesthesia, needle length, and bleeding or nerve irritation symptoms due to the epidural catheter of two groups and the distance of the skin to the epidural space of the ultrasound group. The incidence of post epidural puncture headache and abnormalities of lower extremity sensory or motor after the surgery and the incidence of backache on 1, 3, and 7 d after the surgery were recorded. Results Compared to the control group, the time for locating the interspinous space of the ultrasound group was significantly longer (P<0.01); the success rate of combined spinal and epidural anesthesia performed by one puncture was significantly higher (P<0.01); and the incidence of anesthesia related complications was significantly lower (P<0.01). Conclusion Locating the space between the third and fourth lumbar vertebrae by ultrasound imaging technique is helpful for improving the success rate of combined spinal and epidural anesthesia performed by one puncture and decreasing anesthesia related complications and has certain value in clinical applications.