Abstract: Microstructure of cast iron and casting defects was an important factor that influencing its performance, also was a basic measure of cast iron pressure vessel safety and reliability. But the nondestructive testing technology of cast iron pressure still lacked the mature methods and perfect testing standards in domestic. This article mainly aimed at high speed and wide paper machine drying cylinder of ductile iron head for spheroidization rate and internal defects in ultrasonic testing. It could verify the reliable application of the ultrasonic test in these axes, and predict the organization and mechanical properties of ductile iron by this experiment.