A 600-year integration performed with the Bergen Climate Model and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data were used to investigate the impact of strong tropical volcanic eruptions on the East Asian summer monsoon (EASM) and EASM rainfall. Both the simulation and NCEP/NCAR reanalysis data show a weakening of the EASM in strong eruption years. The model simulation suggests that North and South China experience droughts and the Yangtze-Huaihe River Valley experiences floods during eruption years. In response to strong tropical volcanic eruptions, the meridional air temperature gradient in the upper troposphere is enhanced, which leads to a southward shift and an increase of the East Asian subtropical westerly jet stream (EASWJ). At the same time, the land-sea thermal contrast between the Asian land mass and Northwest Pacific Ocean is weakened. The southward shift and increase of the EASWJ and reduction of the land-sea thermal contrast all contribute to a weakening of the EASM and EASM rainfall anomaly.