Based on the 1945-2008 typhoon data from JTWC, the accumulative cyclone energy ( ACE) over the western North Pacific is calculated. The characters and the relati onship between ACE and SST in NINO3.4 are analyzed. The following results are ob tained. ACE is mostly concentrated in June-December. The activity of ACE occurs at regular intervals. After 1990, the frequency of extreme strong typhoon had a n increasing tendency obviously. The relationship of ACE in June-December and a nomalous SST in NINO3.4 is notable. Abnormal Walker circulation and Hadley cell play an important role in the relationship between ACE and SST.