Abstract: For mechanical equipment with high-speed rotating lubrication such as gearboxes, the failure and oil leakage of the rotating oil seal are common phenomena during the operation process of equipment. In this paper, by analyzing the correlation structure of rotating oil seal in the plunger pump gearbox, various factors which may cause the failure of the rotating oil seal are emerged; analysis and comparative experiments are conducted to verify the preliminary factors so as to find the root cause of the failure of the rotary oil seal. The leakage problem of the rotary oil seal is solved after the targeted improvements are made. The machining process methods for the oil seal position of the mechanical shaft are summarized, and thus the "structural functional analysis" method is formed based on the analysis process.