Abstract: A testing system based on explored ultrasonic TOFD(time of flight diffraction) with USB was presented for thick-walled weld inspection.And the cross-correlation algorithm was used to correct the distorted testing image for defect identification.The system was applied on the boiler weld testing at the workshop.The results show that the D scan image is clear and the defects can be recognized quickly.The distortion of testing image was well avoided by cross-correlation algorithm.The developed system is open,which can be updated according to the requirement.The testing processing can be easily implemented.So the system is suitable for weld detection and could provide referenced data for the quality evaluation of weld.