The device fault generally starts from a minor one and gradually develops to the loss of working capacity of the whole set. Detection in case of a minor fault can recover the unnecessary loss. Therefore, this study proposes a method to evaluate device health status on the basis of the Weighted Mahalanobis Distance (WMD) and the Device Status Index (DSI). Based on an improved Mahalanobis-Taguchi system, the method constructs a stable reference space for the characteristic parameters during the effective operation of the device. It selects the characteristics and calculates the WMD according to the device fault sensitivity, eliminating the interference of characteristic correlation. Then Box-Cox transformation is used to determine the threshold value of the DSI to build a health status model of the complex heavy device, and the model is verified by experiments. The WMD values of the normal samples are all below the fault threshold, and nearly 98.6% of the sample values are within the warning signs. The proposed method can provide data support for maintenance and management of complex heavy devices, thereby facilitating industrial production.