bout 15% of typhoons over the Northwest Pacific Ocean-South China Sea suddenly turn eastward or northward south of 22°N. It is because equatorial anticyclone-equatorial buffer zone over there usually strengthens and moves northward, then induces a burst and strengthening of equatorial westerly. As a result, typhoons are steered and then turn eastward. Calculations show that a typhoon would turn eastward at lower latitudes about 32-20 hours after the equatorial westerly wind speed attains 12-24m/s. A simple numerical simulation is also run in this paper. Typhoon moves normally toward W-NW when the tropical easterly is stronger or slightly weaker than the equatorial westerly; on the contrary, it turns eastward when the equatorial westerly is obviously stronger than the tropical easterly. Some synoptic cases given in this paper verify this viewpoint entirely. The authors emphasize that an important effect of the equatorial westerly-equatorial anticyclone on typhoon movement must be considered carefully. bout 15% of typhoons over the Northwest Pacific Ocean-South China Sea suddenly turn eastward or northward south of 22 ° N. It is because equatorial anticyclone-equatorial buffer zone over there is usually strengthens and moves northward, then induces a burst and strengthening of equatorial westerly. As a result, typhoons are steered and then turn eastward. Calculations show that a typhoon would turn eastward at lower latitudes about 32-20 hours after the equatorial westerly wind speed attains 12-24 m / s. A simple numerical simulation is also run in this paper. Typhoon moves normally toward W-NW when the tropical easter is stronger or slightly weaker than the equatorial westerly; on the contrary, it turns eastward when the equatorial westerly is obviously stronger than the tropical easter. Some synoptic cases given in this paper verify this viewpoint entirely. The authors emphasize that an important effect of the equatorial westerly-equatorial anticyclone on typhoon movement must be con sidered carefully.