Qinghai Lake is of significance for paleoclimate research because it lies in a pivotal region that is influenced by both the mid‐latitude Westerlies and the low‐latitude Asian summer monsoon (ASM). Most published lake level histories of Qinghai Lake are interpreted from drill‐core proxies. Here we combine geomorphic shoreline investigations with optically stimulated luminescence dating to constrain lake level variations since the last deglacial. The results indicate that two periods of highstands occurred during the last deglacial (∼16–14.9 and ∼12.6–12.2 ka), and that lake levels were 6–7.4 m higher than at present. Lake levels dropped abruptly during the Younger Dryas, and were generally low with frequent fluctuations during the early Holocene. Qinghai Lake reached its highest Holocene level, 9.1 m higher than modern, at ∼5 ka, and has regressed during the past 2 ka. We propose that high lake levels during the last deglacial were due mainly to melting glacial and permafrost waters, supplemented by enhanced Westerlies precipitation and decreased evaporation during Heinrich Event 1 (∼16–14.9 ka) and increased ASM rainfall during the Bølling–Alleröd warm period (∼14–12 ka). Lake level fluctuations during the Holocene were generally in accordance with moisture variations in the marginal monsoon zones of inland China.