Hydrographic data acquired in the Taiwan Strait during the past decade suggest that, in winter, a zonal oceanic front develops over the Changyuen Ridge implying that the northward moving Kuroshio branch current cannot persistently hug the west coast of Taiwan as it flows toward the East China Sea as previous suggested. A three dimensional numerical model is used to study the dynamic process leading to the hydrographic pattern observed in the Taiwan Strait in winter. Model results show that the warm Kuroshio branch water in the Peng-hu Channel is blocked and then is forced to deflect westward as it impinges on the southern flank of the ridge. On the other hand, the monsoon-driven southward flowing cold China coastal water spreads southeastward into the northern Taiwan Strait when it passes around the Hai-tan Island. The cold water bulge occupies the upper layer of the area north of the ridge in time as winter progresses. The overall flow behavior in the strait in winter favors the formation of the oceanic front over the ridge between the two water masses.