Abstract: In the dectection of small diameter tube, the coupling and focusing effect becomes the key factor affecting the detection effect. This article analyzed the imaging characteristics of two kinds of transducer for defects, compared the experimental results of two kinds of transducer for the same defect imaging effect, the results show that the cambered array applied in detecting small tube array has better SNR and imaging effect, and the planar array need to increase the compensation equivalent to the cambered array detection.