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We report a 1556 year-long tree-ring width chronology for the Hexi Corridor, in the arid Northwestern China, established by applying the signal-free regional curve standardization method to 416 juniper ring-width series. We found that drought in early summer (May-June) is the primary controlling factor for tree growth in this area. We then developed an early summer moisture (i.e., scPDSI) reconstruction from 455 CE to present. Our reconstruction captures multi-centennial scale moisture variations, showing two long-term dry periods during 800-950 CE and 1000-1200 CE, and two long-term wet periods during 1200-1450 CE and 1510-1620 CE. We found strong similarities between hydroclimatic changes in the Hexi Corridor and Qaidam Basin from interannual to centennial timescales; however, at multi-centennial (>300 years) timescales, hydroclimatic variations in the two regions showed significant regional differences. The Hexi Corridor witnessed a generally dry Medieval Climate Anomaly (MCA, here 800-1200 CE) and the drying 20th century, whereas the Qaidam Basin experienced high-precipitation periods during the MCA and 20th century. The different correlation pattern with Northern Hemisphere temperature suggest that the Qaidam Basin will receive more precipitation under global warming, whereas the Hexi Corridor will become dryer in the future.