The beet armyworm, Spodoptera exigua Hübner (Lepidoptera: Noctuidae) is a serious agricultural pest worldwide. However, population sources of S. exigua in outbreak regions are still vague due to the lack of understanding the distribution of overwintering regions, especially in China. In the present study, the potential overwintering regions of S. exigua in China are projected using the method of Compare Location in the CLIMEX model in order to understand the population sources in outbreak regions and establish an accurate forecasting system. The results showed the southern and northern overwintering boundaries near the Tropic of Cancer (about 23.5 ^°N) and the Yangtze River valley (about 30 ^°N), respectively. Meanwhile, the projection was supported by the data of fieldwork in 14 countries/cities during winter from 2008–2010. In conclusion, results of this study indicated that the overwintering regions of S. exigua were accurately projected by the CLIMEX model.