The characteristics and attribution of the spatiotemporal variation of the Asian summer monsoon (ASM) precipitation are not sufficiently understood, especially on multidecadal-centennial time scale. In recent years, climate model has been an important and effective tool to solve the problem. In this paper, we compared six experiments conducted for the past 2000 years using the Community Earth System Model (CESM, version 1.0.3) to analyze the characteristics and causes of the precipitation variation of ASM (5°~55°N, 60o~170oE) and its sub-systems on centennial time scale. The experiments include total solar irradiation experiment (TSI), volcanic eruptions experiment (Vol), greenhouse gases experiment (GHGs) and land use/land cover change experiment (LUCC),control experiment (Ctrl) and all forcings experiment (ALL). Five experiments are carried out from 1A.D. to 2000A.D. based on a 2400 years' control experiment under the A.D. 1850's initial forcing. Limited by the reconstructed volcanic data, the volcanic eruptions experiment starts from 501 A.D. and there is no volcanic forcing during 1~500A.D. in the all forcing experiment. Based on the comparison of simulated results derived from all forcings experiment with proxy records and reanalysis data, the performance of CESM in simulating climate change over Asia was verified. By the way, the sub-systems of ASM include East Asian summer monsoon (EASM, 20°~ 55°N, 105°~140°E), Indian summer monsoon (ISM, 5o~40oN, 60°~105°E) and the western North Pacific summer monsoon (WNPSM, 5°~25°N, 105o~170oE). The precipitation and temperature mainly reflect an in phase variability on centennial time scale both over the ASM region and its sub-regions. The results of spectrum analysis show that there are three periodicities (100-yr, 150-yr and 200-yr) in the ASM precipitation, two periodicities (100-yr and 200-yr) in the EASM precipitation and the ISM and WNPSM precipitation both have a significant 100-yr period. Compared with the results of other experiments, it can be found that the total solar irradiation is the main factors of the centennial cycle of summer monsoon precipitation over these regions. Also, the volcanic eruptions are related to the centennial cycle of EASM and ASM precipitation. Then the empirical orthogonal function (EOF) is used to find out the spatial characteristic of precipitation. The spatial structure of the first mode of the ASM precipitation (EOF1) shows the plus-minus-plus-minus zonal belts over the east part of 100°E while it shows the plus-minus-plus structure from southwest to northeast over the ISM region. Meanwhile, the spatial structure of the second mode (EOF2) shows negative value over the eastern Arabian Sea, the southern Indian peninsula, the North China Plain and the east region of the plain of the same latitude and shows positive value over other regions. The following results are obtained by comparison with other experiments: The main cause of the spatial pattern of EOF1 is the total solar irradiation and the factors affecting the spatial structure of EOF2 are the greenhouse gases and the internal variability of climate system. At the same time, the nonlinear interactions between diverse factors are found to amplify the influence on the internal variability of climate system. The structures of the main modes of precipitation over three sub-systems are similar to the pattern over the same regions of the EOF1. The first mode of EASM precipitation affects by the total solar irradiation and the greenhouse gases, and the first mode of ISM precipitation is related to the total solar irradiation. Meanwhile, the first mode of WNPSM precipitation is related to diverse factors, except the volcanic eruptions. More works are needed to analyze the external forcing's influence mechanism to ASM precipitation.