To evaluate the fault correlation of machining center system components, by using the related fault mechanism analysis combining graph theory, a method of transfer directed graph of system components fault is built up, the correlation evaluation of system components is converted to the calculation of complex network node importance, and by the adjacency matrix and its transpose transform combining PageRank algorithm, the CNC machining center fault correlation method is obtained. The calculation results show that the size of fault correlation and the relation of component fault correlation is proportional, and the fault correlation of the fault correlation component is greater than those components with no fault correlation. If the influenced degree of a component is larger than its influencing degree, it is the fault appearance component, on the contrary, it is the fault source component. This helps to the fault diagnosis and maintenance.