Abstract: In the oil, gas and chemical industries, the floor of many large containers and oil tanks stored corrosive liquid is easily thinned or pierced by corrosion after long time service. Ultrasonic guided waves could be applied to quickly scan on large defective plate. The guided waves of multifunctional ultrasonic testing instrument was used, which was scanned on 8mm thickness plate of artificial standard flaw by linear and angle ways, using sound signal position device helped probe and flaw position, and presenting planar image. The result of experiment reflected the spread characteristics and testing capability towards diverse flaws of guided waves which were stimulated by definite product of frequency by thickness. The testing results was of great use to the spot testing.