Thirteen tropical cyclones tracking westward at high speed into the South China Sea are analyzed. It shows that the major characteristics of the westerlies is that from Middle Asia to East Asia was covered by a ridge or zonal circulation and westerly troughs were at higher latitudes. The results also show that a constantly intense zonal spreading subtropical high dominated from the west North Pacific to central and southern China or a continually strengthening subtropical ridge that extending westward gradually built up the gradient between the ridge and tropical cyclone and strengthened the easterly steering flows. Moreover,the easterly environmental flows prevailing in both of the southern and northern sides of tropical cyclone would drive it to travel more quickly.