Abstract: The poloidal field(PF) coils in ITER Tokamak device require a lot of superconducting cables in conduit conductors(CICC), stainless steel conduit tube is an important part of the CICC as it is the container of cooling liquid Helium and supporting structure of the electromagnetic load. To ensure the safety of the PF coil, nondestructive testing has to be performed for each conduit tube of CICC. However, because of outer square inter round cross section shape of the PF stainless steel conduit tube, the domestic corresponding NDT method hasnt established, so need to develop new testing system. Aiming at this problem, the approach of immersed ultrasonic testing method using single focus transducer or phased array probe was proposed, and through fabricating samples with artificial defects, the validity of this approach was verified. The experimental results showed that the approach was promising for the NDT of the ITER conduit tubes.