Based on JTWC tropical cyclone data, NCEP reanalysis data and Hadly Center SST data, the abnormal year’s climatic features and background for accumulated cyclone energy (ACE) over the Northwest Pacific are analyzed. The results show that ACE has significant interannual and interdecadal variations. In the abnormal years of ACE, due to the notable difference of the longitude that the eastern flow from monsoon trough reaches, the passageway and intensity difference of cross equatorical flows, and the location difference of subtropical high, the frequency, intensity and the persistence of typhoons are different. The abnormality of ACE is closely connected with tropical Pacific SSTA in May-August. When SST anomaly at equatorial central and eastern Pacific is positive and that of Southwest Pacific is negative, as a result of favorable cross equatorical southern flow provided by downflow branches of abnormal Walker and Hadley Circulations, the year’s ACE tends to be positively abnormal. Otherwise, ACE tends to be negatively abnormal.