By analyzing Soil Moisture Anomaly Percentage Index （SMAPI） at different soil layers， dry-wet evolution of the source region of the Yellow River （SRYR） during 2008 -2017 are investigated using observations from the Maqu-Ruoergai soil temperature and moisture monitoring network.To diagnose the water vapor transportation path and potential water vapor sources in different processes， the Lagrange Flexible Particle Dispersion Model （FLEXPART）， which is driven by reanalysis data （National Centers for Environmental Prediction Final， NECP FNL）， are used to simulate the backward trajectories of target particles.The results show that the water vapor transportation path can be divided into three categories： （1） South Branch transportation.The water vapor origins from the Indian Ocean and the Arabian Sea， and finally arrives at the SRYR by way of the Indian Peninsula and Bay of Bengal； （2） East Branch transportation.The water vapor is from the Pacific Ocean and the South China Sea， then passes through the Yangtze River Basin， and finally arrives at the SRYR from eastern and southern flank of the Tibetan Plateau； （3） North Branch transportation.The water vapor is from the Atlantic Ocean， the northern African continent， and the European continent， then arrives at the SRYR from the western or northern side of the Tibetan Plateau by way of the mid-latitude Eurasian continent.Moreover， the North Branch is dominant in dry period， whereas the South and East branches are prominent in wet period.The water vapor sources also show discrepancies for dry and wet periods.The water vapor sources of the Tibetan Plateau are mainly distributed around the Kunlun Mountains during wet period， and are scattered distributed from north to south during transitional period， and are located around the Tianshan during dry period.The intensity of the water vapor sources of the Iranian Plateau， Pamir Plateau， and the Bay of Bengal gradually strengthen from wet to dry period， the intensity of the water vapor sources of the Sichuan Basin-Qinling Mountains and south China enhanced first and then weakened， while the source of Qilian Mountain-Loess Plateau weakened after enhanced.The intensity of water vapor sources over the middle and lower reaches of the Yangtze River and around East China has been weakening from the wet period to the dry period.