Aiming at the problem that the bimetallic composite plate may produce defects during the processing of fabrication and usage, the principle of ultrasonic phased array detection and the theory of radiation sound field are introduced in this paper. Through the experiment research on the stainless steelcarbon steel specimens with the crossdrilled hole of 3 mm and corrosion pits, it is found that the ultrasonic phased array technology can measure the artificial defects in the stainless steel-carbon steel by real-time imaging, the location and size of defects can be accurately obtained and the measurement errors of the two kinds of defects are less than 6% and 12%, respectively.