Human reliability has been a focus in system reliability and safety researches since 1960s, and now human factor has become an increasingly important reason which affects system reliability. Numerical control machining system characterized by man-machine interaction can be applied to automatic parts machining with high efficiency. However, professional and technical staffs are still needed for clamping, positioning, inspection and others. So there is no doubt that the quality of the parts might

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... be influenced by personnel behaviour. What's more, on-site staff is responsible for handling potential fault directly. The study on human error plays an important role to ensure the quality and reduce industrial accident. Holistic Decision Tree (HDT) is a dynamic Human Reliability Analysis (HRA) method, emphasizing the wholeness of man-machine interaction. This paper tries to use an optimized HDT method to investigate human reliability in numerical control machining system. In order to obtain a rational order of the importance of each IF, this paper incorporates entropy weight method to the conventional expert method to determine the relative weight value of each human behaviour influence factor (IF), and finally calculates the human error probability (HEP).