Abstract: Abstract Ductile iron casting (DCI) main shaft is a key component of wind turbine, it has thicker wall and higher material designation, which have to bear enormous and complex load after assembly. In order to ensure the well-running of wind turbines in the whole life cycle, the surface and internal quality shall not only meet the acceptance standards by normal nondestructive testing methods, but also the overall density and homogeneity of material as well as co-related mechanical properties shall to be tested and verified. Based on the physical standard test block verification and DCI casting theoretical knowledge, ultrasonic phased array PCI technology was adopted to fully inspect the DCI shaft. After data analysis and results comparison, this paper confirmed that this method could determine the depth of rapid cooling layer of chills used in shaft accurately and evaluated the coarse grain condition of thick-walled ductile iron castings preliminarily.