As an important part of CNC machine tools, machining center's reliability, efficiency and accuracy measure the machining level of a CNC machine tool. Therefore, the research on the importance of CNC machine tools is particularly important. However, as a complex mechanical and electrical equipment, the traditional reliability importance analysis method is too simple. In order to solve this problem, this passage proposes to establish the reliability model of each part of the machining center, and then analyze its dynamic importance, which improves the limitation of only reliability importance analysis. Through the analysis the reliability importance and criticality importance, and then rank the result of importance analysis, finally it can get that the ranking results of the key components accord with the fact, so the results can provide support for the importance research of machining center.