Abstract: The characteristics and causes of the centennial variation of Asian-Australian summer monsoon precipitation over the past 2000 years are investigated using the Community Earth System Model (CESM). The results of the simulation are verified based on model-proxy data comparison and model-observation data comparison. This research is important for recognizing centennial climate variation and distinguishing between the influences of natural and anthropogenic climate change signals on the Asian-Australian summer monsoon. The results show that the variation of precipitation and temperature in summer of Asian-Australian is consistent over the past 2000 years. More precipitation occurs in warm periods and less occurs in cold periods. The correlation coefficient of precipitation and temperature is 0.83, which is significant at the 99% confidence level. In addition, it is found that the Asian-Australian summer monsoon precipitation varies on three centennial periods (105, 130 and 180 a). The spatial structure of the first leading mode of empirical orthogonal function (EOF) of Asian-Australian summer monsoon precipitation shows a reverse pattern in the north and south of the northern Indian Ocean and a negative-positive- negative pattern in East Asia. The spatial structure of the second leading mode of EOF shows a positive-negative-positive pattern in the northern Indian Ocean and an almost in-phase variability in East Asia. The positive and negative centers of the first and second leading modes of EOF are mostly located in the northern Indian Ocean, and the spatial structures are asymmetric between the Northern and Southern Hemispheres. The 105 a cycle of the Asian-Australian summer monsoon precipitation is mainly caused by volcanic eruptions and land use/cover. The 130 a cycle of the Asian-Australian summer monsoon precipitation is mainly caused by total solar irradiation and internal variability of the climate system. The 180 a cycle of the Asian-Australian summer monsoon precipitation is mainly caused by volcanic eruptions. In terms of the first EOF mode, the variation of the Asian-Australian summer monsoon precipitation is mainly affected by land use/cover and total solar irradiation. The second EOF mode shows that the variation of the Asian-Australian summer monsoon precipitation is mainly affected by total solar irradiation and internal variability of climate system. The third EOF mode shows that the variation of the Asian-Australian summer monsoon precipitation is mainly affected by internal variability of the climate system and greenhouse gases. This research not only reveals the characteristics of centennial variability of climate, distinguishes between natural and anthropogenic climate change signals, and helps us to understand the mechanisms for climate change, but also provides a scientific basis for responding to climate change in the study area.