Abstract: The UT method and procedure of marine cast steel by the normal twin transducer probe were detailed in order not to have the exposed defect on the surface of work after finishing, and consequently to meet the request of the work. The concept for defect of honeycomb profile has been introduced in the article, 3 kinds of reflective waveform for defect of honeycomb profile(airhole type, shrinkage cavity type and slag type) were analyzed mainly. The following conclusions have been testified: this method is useful to internal defects evaluating of marine cast steel; this method with watching echodynamic patterns of defect is useful to locate and quantify and be qualitative quickly for defect; the method with 2~4 MHz, 14~20 mm focus of Normal twin transducer probe in  3 sensitivity can be sure to the defect not appearing on the surface of work after finishing.