Abstract: Described in the article are the contact method and the water immersion method for detecting the extraheavy wall seamless steel tube.Also analyzed is the sonic beam-coverage area of such tube.It is regarded via the analysis that in case that the t/D of the steel pipe is greater than 0.26,neither the pure shear wave method nor the modified shear wave method can detect the defect on the inner surface,and therefore the“small angle refraction longitudinal wave+refraction pure shear wave”process is used to detect the longitudinal defect of the pipe,and the dual-probe detection process in fact,means that for the inner circle(r~0.5R)part of the pipe section,the longitudinal wave detection is adopted,while for the outer circle(0.5R~R)part of the pipe section,the shear wave+longitudinal wave detection is adopted.