Many lacustrine chronology records suffer from radiocarbon reservoir effects. A continuous, accurate varve chronology, in conjunction with accelerator mass spectrometry (AMS) 14C dating, was used to determine the age of lacustrine sediment and to quantify the past 14C reservoir effect in Sugan Lake (China). Reservoir age varied from 4340 to 2590 yr due to 14C-depleted water in the late Holocene. However, during the Little Ice Age (LIA), 14C reservoir age was relatively stable. According to this study, 14C reservoir age in the late Holocene may be driven by hydrological and climatic changes of this period. Therefore, special caution should be paid to the correction of the 14C reservoir effect by a unique 14C reservoir age in paleoclimatic and paleolimnological study of northwest China.