Tropical cyclone (TC) activities over the western North Pacific and the South China Sea in 2015 have such characteristics as so many typhoons in winter and spring, so few typhoons in the South China Sea, generated source is easier than usual. Based on NCEP/NCAR reanalysis data, and the Outgoing Long wave Radiation (OLR) data from NOAA, some primary researches are performed. The results show that the abnormal warmer SST in the western North Pacific and the South China Sea is the key factors in TC abnormal activities; and external forcing of sea surface temperature anomalies caused by Walker circulation ascending area is located in the central and eastern equatorial Pacific, the vast west Pacific is a descending area, the Pacific subtropical high strengthens and spreads westward, East Asian summer monsoon is weak, ITCZ location is southerly, abnormal heat is easterly, which leads to the TCs generated source is easier than usual and TC number in the South China Sea is less than normal.
