Abstract: All involved in the paper is how to select proper probe angles for the contact type ultrasonic detection system for steel pipes.According to the three pipe thickness/diameter ratios or T/D's, the probe angles are determined respectively.Based on relevant analysis, it is identified that in case of T/D ≤ 0.226, pure transversal wave will be used to detect the pipe body;in case of 0.226<T/D ≤ 0.260, transformed transversal wave will be used to detect the pipe body with the best angle of incidence as 23.6°;and in case of T/D>0.260, the probe angle will be less than the best incidence angle of 23.6°.