A research about the ultrasonic phased array imaging principle from A-scan signal to B-scan image for nondestructive testing (NOT) was conducted in this paper, the ultrasonic phased array inspection imaging system used in industrial field was developed and the experiment was performed on the steel testing black by the system with 64 elements, 5 MHz phased array transducer. Experimental results show that the flaws could be accurately detected and the flaws size could be estimated from the B-scan images, and the B-scan images could clearly show the location of the flaws, hut the quality of B-scan images needs to be enhanced by digital signal processing and controlling dynamic focusing for improving the image resolution.