The erosion behaviors of a hydraulic concrete under high-speed abrasive waterjets at different impact angles were investigated in this paper. The worn surfaces were observed by a scanning electron microscope (SEM). It was found that the defects in the matrix are often the nucleation sites of the microcracks during the erosion. The erosion mechanisms of hydraulic concrete at different impact angles were discussed. The results showed that the erosion process is mainly the microcutting at small impact angles, but peeling off at large impact angles, or mixed mechanism, i. e. microcutting and peeling, at medium impact angles.