In this paper,the ultrasonic scanning detection method of carbon fiber reinforced composite（CFRP） joints in the bogies of electric vehicles is studied. The defect information is collected by ultrasonic C-scan method,and a manual ultrasonic imaging detection system is established for carbon fiber reinforced composite connectors,which avoids the technical drawbacks of poor adaptability of conventional ultrasonic automatic scanning imaging to irregular surface structures,and makes the detection process real-time,fast and flexible. Based on the KSW entropy method,a geometric model is established and two three-dimensional models are built. The defect coverage area and the defect coverage rate are obtained by the computed program. The visualized defect detection in the three-dimensional image of the component is realized,which avoids the naked eye observation in the conventional method and improves the reliability of the detection results.