The morphological feature information of the slipper wear fault and the swash plate wear fault with the same harmonics is in high similarity, so it is difficult to effectively separate the coupling fault. In order to solve the problem, a new mathematical morphological separation method based on laddershaped structure element was proposed. Two kinds of fault feature information were extracted by using morphological difference operators with different lengths of laddershaped structure element, and then several separated signals corresponding to different lengths laddershaped structure element were obtained; the feature energy ratio (FER) of the two different faults of the separated signals were calculated. Based on the maximum FER, coupling fault signals of the slipper wear fault and the swash plate wear fault of hydraulic pump can be separated in the best way.