Abstract: Aiming at the technical difficulties of time of flight diffraction(TOFD) testing on eccentric flaws in butt weld joints, the ultrasonic field was researched, and the impact of eccentric flaws to TOFD testing was concluded. Through the relevant experiments, the results of parallel scan and non-parallel scan were compared, and it concluded that the eccentric flaws could be determined by the method of the combination of non-parallel scan with parallel scan and eccentric non-parallel scan.