To solve shortcomings of traditional hierarchy directed graph method when applied to satellite ground station fault diagnosis, the EHDG (enhanced hierarchy directed graph) fault diagnosis method was proposed. In process of modeling, considering large number of fault symptoms and complex modeling, nodes of the same kind were consolidated according to the fault propagation paths of devices working status to reduce the scale of the model. Furthermore, the node effectiveness enabling function was introduced into the model to overcome the problem of remodeling in the traditional hierarchy directed graph model when the system structure was changed caused by the active/standby switching of device. In process of fault diagnosis reasoning, the search space of fault source was reduced by the combination of backtracking and forward reasoning method. The fault probability was calculated with the number of search hits of the nodes in order to enhance the efficiency. Fault diagnosis method in single fault and multiple faults scenarios of BeiDou radio determination satellite service ground station system was verified, and the results demonstrate that the EHDG method improves the accuracy and comprehensiveness in fault diagnosis.