In the house of availability (HOA) of complex products, the accurate calculation of the autocorrelation coefficient of fault factors is conducive to obtain the accurate weight of the fault factors, which is targeted at establishing the availability guarantee mechanism. Therefore, this study presents a method, which considers a number of expert opinions and influencing factors, to figure out the autocorrelation coefficient of fault factors. The fuzzy causal relationship between the fault factors are expressed as an extension interval number, which is converted into the determined value using the extensible analytic hierarchy process(EAHP). Then, the autocorrelation coefficients between the fault factors are obtained. The method considers all of the various influence factors of the fault factors and their fuzziness, which ensures that the accuracy of the calculated autocorrelation coefficients is high. Finally, the method is validated by using a series of machining centers as an example.