Abstract: At present, the traditional film photography is used to detect the welding seam of the bottom, barrel and ring parts of the launch vehicle, which has the disadvantages of low automation, complicated process and low digitization, and the negative film can't be preserved for a long time, so it can't meet the fast-paced development requirements of the current multi-type rockets. A robot-based multi-degree-of-freedom digital radiographic inspection system was developed by using the nondestructive inspection method combining X-ray and imaging board, using double seven-axis robot and synchronous lifting turntable as motion actuators, and using ADS multi-thread communication and Ethercat bus to realize the real-time communication among the controller, imaging inspection software, X-ray machine, robot and synchronous lifting turntable. Through the path planning of the motion actuator and the nondestructive inspection of weld seam imaging, the inspection automation of circumferential seam, longitudinal seam and variable curvature weld seam of products is realized. Compared with the traditional film photography, the inspection efficiency is increased by 5 times and the inspection accuracy is increased by 42%, which meets the current inspection work of multi-model rocket tanks.