This paper aims to analyze the effect of appurtenant structures on the seismic response of arch dams. For this purpose, a fine-grade finite element model is developed for the Sanhekou dam in China as a case study, which includes the discharge structure, the intake tower, the elevator shaft, and the viewing platform. The results indicate that different appurtenant structures have different influences on the seismic response of the dam. The crest spillways and the low-level outlets perforated in the dam body, significantly affect the seismic response of the local region of the arch dam body, while the appurtenant structures extending from the dam body, such as the intake tower, the elevator shaft, and the sightseeing buildings, have little influence on the seismic response of the dam body. In addition, the local vibration amplitudes of the high cantilever water inlet and the high-rise elevator shaft are significant, and thus they may be damaged under seismic loads.