In this article a commercial controller communication module is used to capture the cutting machine's processing path, position feedback, position error, feed speed and other information, output the four types of quantitative indicators, including machining path error, NC error, servo error, and tool end vibration error and carry out the defect cause analysis based on the largest proportion. During the cutting process, a digital twin model is created simultaneously, and the cause and value of the defect are marked in the model. Engineers can more intuitively analyze the location, cause and value of the defect, so that it can be confirmed whether the location is important, how to improve, or can be ignored.