Knowledge of moisture sources is of great significance for understanding climatic change and landscape evolution in desert environments.In this paper,we aim to clarify moisture origins for the Alashan (Alxa) Sand Seas (ALSS) in west Inner Mongolia and their transport pathways during the Last Glacial Maximum (LGM) and the mid-Holocene using mod analogues and paleoclimatic simulations.Precipitation data for the period 1959-2015 from meteorological stations in the study area and wind and specific humidity data from the European Center for Medium-Range Weather Forecasts (ECMWF) daily reanalysis were adopted to determine the moisture sources of summer precipitation in the ALSS.In addition paleoclimate simulations under PMIP3/CMIP5 protocols were used to detect the atmospheric circulation and precipitation at 21 ka BP and 6 ka BP over the ALSS.We also reviewed paleoclimate records from the ALSS to acquire a semi-quantitative reconstruction of the moisture history during the late Pleistocene and Holocene.Our results suggest that the summer monsoon transported water vapor from the Indian Ocean and the South China Sea to the ALSS during July and August,causing increased precipitation.The dominant moisture source was from the southwest monsoon,while the East Asian summer monsoon also partly contributed to precipitation in the ALSS.The increased humidity during the period 8.2-4.2 ka BP in the ALSS,as derived from both climate simulation outputs and sedimentary records,was caused by monsoons according to the outputs of simulations.At 21 ka BP,the moisture sources of the ALSS were greatly associated with the prevailing westerlies.