Abstract: Abnormal spots were found on the fuel pump impeller during the return check. In order to find out the cause, a scanning electron microscope (SEM), an optical microscope (OM) and an energy dispersive spectrometer (EDS) were used to analyze the morphology, microstructure and chemical composition of the abnormal spots. In addition, the working principle of the fuel pump impeller was analyzed. The results show that the abnormal spots were mainly caused by cavitation erosion due to the unproper clearance between the impeller and the shell and the sharp corner at the blade edge. There are many pits at the abnormal spots. The inner walls of the pits are smooth and clean. The features of microscopic plastic deformation are obvious. These features are the main morphological characteristics of cavitation erosion damage.