Total focusing method imaging is a phased array (PA) post-processing imaging method based on full matrix acquisition data with high resolution and high signal-to-noise ratio. However, the placement of the probe is largely limited by the shape of the detection surface. In this paper, a water membrane PA probe that can perform in-service detection of unknown interface objects in indirect water immersion mode is used, and a covariance correlation weighting factor for optimizing adaptive Total focusing method (ATFM) imaging results is proposed. Experiments of artificial test block and actual wheel rim have shown that the ATFM can not only identify the profile of the unknown interface, but also image the interior of the test object. Furthermore, the contrast signal-to-noise ratio of the defect signal is increased by 40 dB on average, and the defect resolution is also Improved. This method, meanwhile, can truly reflect the morphology of internal defects in actual inspection objects, which is conducive to non-destructive evaluation of defects.