The Yellow Sea Warm Current (YSWC) penetrates northward along the Yellow Sea Trough, and brings warm and saline water towards the Bohai Sea. The YSWC becomes much less intrusive in summer and is limited mostly in the south trough, contrasting with a deep winter penetration well into the trough. The seasonal variability of the YSWC has prompted a debate regarding which controls the YSWC and its seasonal variability. In this article, the annual mean and seasonal variability of the YSWC was examined by using a 3-D ocean model together with several experiments. The results show that in the annual mean the YSWC is a compensating current firstly for the southward Korea Coastal Current (KCC), which is mainly caused by the Kuroshio Current (KC). The local wind-stress forcing plays an important but secondary role. However, the local monsoonal forcing plays a prominent role in modulating the seasonal variability. A deep northwestward intrusion of the YSWC in winter, for instance, is mainly due to a robustly developed China Coastal Current (CCC) which draws water along the Yellow Sea trough to feed a southward flow all the way from the Bohai Sea to the Taiwan Strait.