Abstract: The variable cross-section cast steel parts are common parts in high-speed trains, and it is very difficult to apply X-ray radiographic inspection to it. But fortunately, the X-ray DR system could acquire richer original image; the continuous exposure Log-calculation or the images averaging could decrease the noise; the scattered radiation shield could improve the signal to noise ratio; the logarithmic demodulation could enhance the image details; and the digital radiography could get wide dynamic range, and have excellent Latitude. By using all these methods and technologies, we successfully tested various defects of the cross-section steel castings in the high-speed train.