Based on observational and reanalysis datasets during 1957-2017, this study compares the impact of different phases of the Pacific Decadal Oscillation (PDO) on seasonal and intraseasonal variation of the East Asian summer monsoon (EASM) in El Ni?o developing years and La Ni?a years. Results show that PDO positive (negative) phase reinforces El Ni?o developing (La Ni?a) behaviors mainly via modifying the background EASM circulation, precipitation and intraseasonal variation. When El Ni?o is in phase with PDO (El Ni?o/ high PDO), PDO amplifies the warm sea surface temperature (SST) anomaly signal of the central and eastern Pacific during the summer, besides it strengthens the mid-high latitudes circulation anomaly of the East Asia continent and the Northwest Pacific through the cold SST state. In La Ni?a years, the negative PDO phase promotes the tropical air-sea interaction and also causes the circulation anomalies in mid-high latitudes, such as an anti-cyclonic anomaly in northeast Asia. With respect to intraseasonal variations, during the June of El Ni?o developing years, there exist stable northerly anomalies from anti-cyclonic circulation east of Lake Baikal, which induces negative geopotential height anomalies over East Asian. Since July, the circulation has been adjusted, cyclonic anomaly has appeared in the eastern ocean of Japan, besides the northerlies and negative geopotential height anomalies have been strengthened. In August, with the seasonal march of EASM seasonal and the development of El Ni?o, cyclonic anomaly occurs in the Western Pacific Ocean, the subtropical geopotential height further reduces and the western Pacific subtropical high (WPSH) retreats eastward clearly. In La Ni?a years, the circulation anomalies are weak in June. The main differences begin with July, characterized by the large-scale cyclonic anomaly control in the Northwest Pacific Ocean and the significant East Asia-Pacific teleconnection pattern, which eventually weakened the WPSH and retreated it eastward. As a result, there was less summer precipitation in both cases over East Asia especially in northern China.