Recent studies have found a connection between Indian Ocean Basin Warming and the anomalous Northwest Pacific Anticy- clone （ANPWA） during El Nifio decaying year. This study focuses on the necessary condition for this connection by using ob- servation and numerical simulation. The seasonal transition of the Indian Ocean sea surface wind is critical to the climatic ef- fect of Indian Ocean Basin Warming. When the South Asian Summer Monsoon reaches its peak, the background wind be- comes desirable for basin warming, which then affects the climate in the Northwest Pacific. Via the Kelvin waves and Ekman divergence, the wind anomalies exist in the lower atmosphere east of the Indian Ocean warm Sea Surface Temperature （SST） anomalies, and intensify and sustain the ANWPA throughout the E1 Nifio decaying summer. This impact plays an important role in the inter-annual variability of the East Asian Summer Monsoon.
