Abstract: According to the 14-year (1967-1980) midsummer wind data and 9-year (1972-1980)geo-potential height data we found that during the midwinter in Southern Hemisphere, when the long-wave trough over the east coast of Australia is located farther west (about 170°E),the westerlies over this area is strong while that over the eastcoast of Asia is weak, the typhoons over NW Pacific may be more than usual. On tre contrary, when the location of long-wave trough is located farther east (about 150°W), the westerlies over the east coast of Australia is weak and the westerlies over the east coast of Asia is strong, correspondingly the typhoons over NW Pacific may be less.