In order to improve the correction rate of fault diagnosis, one method of mechanical fault diagnosis based on complex three-order cumulants was proposed. The complex forms with different definitions of three-order cumulants included different coupling information of signals, which was used to diagnose fault. In the experiment on the fault diagnosis of overflow valve, using the different coupling information, the features of fault signals and normal signals were extracted by 2-D wavelet in different directions, and then they were input into support vector machine to diagnose the fault. The experiment results show that this method can improve the correction rate of diagnosis. Furthermore, the same experiment was performed on the real three-order cumulants, and the results verify the effectiveness of the method proposed in this paper
