As the most important sources of heat and moisture, the Western Pacific Warm Pool(WPWP) strongly affects regional hydroclimate variability across the world through teleconnections. The variation of precipitation isotope composition over the WPWP and associated mechanisms are crucial for understanding of hydroclimate in the region, but little work has been done on this aspect. In this study,we combine Global Network of Isotopes in Precipitation (GNIP),coral delta~(18)O observations and IsoGSM model simulations to investigate the responses of precipitation isotope over the WPWP to the Indian Ocean Dipole (IOD) and underlying mechanisms. By means of various statistical analysis methods, such as composite analysis and correlation analysis, IsoGSM delta~(18)O, coral delta~(18)O, Sea Surface Temperature (SST),Outgoing Longwave Radiation(OLR),precipitation and 850 hPa wind are studied. The results show that during the positive IOD period,the WPWP is dominated by lower sea surface temperature (SST) anomaly, which strongly suppresses the convection and leads to a decrease in rainfall in the region. This reduction in rainfall is further strengthened by a weakening of the Indian Ocean Walker circulation due to enhanced east-west SST gradient over the tropical Indian Ocean. These have resulted in reduced rainout and thus higher rainfall delta~(18)O values in the WPWP. The opposite conditions occur during the negative IOD period. The impact of the IOD on rainfall isotope is also reflected in coral delta~(18)O records in the WPWP,which are significantly positive correlated with Dipole Mode index(DMI, an index for IOD strength). Climate model projects a more positive IOD due to global warming,which means that the stable isotope composition in rainfall and corals in the WPWP will evolve towards a more positive trend in the twenty-first century.