Based on the OLR (outgoing longwave radiation) data from NOAA and the NECP/NCAR reanalysis data along with CMAP precipitation data,using composite analysis and other methods,this paper has investigated the interdecadal change in relations of convective activities between the tropical Northwest Pacific(10°-20°N,125°-140°E) and the tropical Southeast India ocean(5°-15°S,90°-105°E).The results demonstrate that there are significant interdecadal variations in relations of convective activities between the tropical Northwest Pacific and the tropical Southeast Indian Ocean,with a significant positive correlation period from 1980s to 1990s,and a significant negative correlation period from 1990s to early twenty-first century,and another positive correlation period after 2004.When the convective activities in the tropical Northwest Pacific and the tropical Southeast Indian Ocean are positively correlated,there are two anti-cyclonic circulations over the two regions,which lead to weak convective activities and negative precipitation anomalies in the two places.When the convective activities in the tropical Northwest Pacific and the tropical Southeast Indian Ocean are negatively correlated,the distinctly different circulation anomalies are observed in the two regions.Accordingly,during the negative correlation period,the positive sea temperature anomalies are found in the tropical Southeast Indian Ocean,where the upper level divergence and lower level convergence facilitate the anomalous strong convection activities and more than normal precipitation.This scenario is opposite in the tropical Northwest Pacific.The slanted vertical circulation between the tropical Northwest Pacific and the tropical Southeast Indian Ocean connects the two regions,which induces the negative correlation between convection activities over the two regions.