During materials manufacturing process will cause defects occasionally, if the defects located at near surface of material where the testing is not easy to implement. When the defects was stress by outside loading, it will grow up even become fracture, if the material apply ultrasonic testing then can increase material security to ensure structural safety. Practice material defect shape is variable and need complex product procedure. In this study, using wire cutting method to make practice defects specimen instead of the real flaws material, the specimen was made of medium carbon steel and aluminum alloy, defects away from the surface is 2-4 mm, defect shape including round shape hole and square shape hole, bore diameter was 1-3 mm. Using ultrasonic straight beam probe and delay line probe, straight beam probe have 5 MHz and 10 MHz frequency, and delay line probe have 5 MHz, 10 MHz frequency too, finally, compared the relationship between the accuracy and depth of flaws, pore size, flaw shape, material of specimen. Research results demonstrate that accuracy didn’t relate to the flaw shape, flaw size, depth of flaws and material of specimen. The accurately of 10 MHz delayed probe shown the depth of flaw smaller, the measurement than other probes.