Abstract: In order to get the relationshipe of beam path to front distance(l0) and K value of angle probe, some experiments with different beam path length were designed. Testing on the standard block CSK-ⅠA, CSK-ⅢA and SGB showed that, the measuring precision of l0 and K value was affected by the beam path length of reference reflector. When testing was carried on near field zone, the contiuity of l0 was good, and the area of crystal would affect K value also. Means to get more accurate l0 and K value was analyzed in those experiments and it was very helpful to ultrasonic testing.