Impacts of Rossby wave activities on the evolution process of the East Asia/ Pacific (EAP) events during the post-Meiyu period are investigated on the medium-range time scale. The life cycles of positive and negative EAP events cannot be simply regarded as “mirror” each other, but the same structure of westlies waveguide makes them bear some similarities in terms of the dispersion of Rossby wave energy. In the upper and middle troposphere, Rossby wave packet, which is originated from the upstream northeastern Atlantic or East European plateau, propagates through Lake Balkhash, and then turns northeastward to northeastern Asia. It plays an important role in the formation and maintenance of the northeastern Asian anomaly center of the EAP event. Due to the northward shift of the East Asian jet during this period, North China-Northeast China becomes the waveguide area. As a consequence, Rossby wave packets emanating from Lake Baikal propagate to this waveguide area, leading to the formation of the East Asian mid-latitude anomaly center. Among the three anomaly centers, the northeastern Asian one appears foremost, while the western Pacific subtropical one is lattermost. Along the East Asian coastal region, the reversed meridional propagation of Rossby wave packets in the upper and lower troposphere results from the distinct difference between the westerly waveguide structures of the upper and lower troposphere. The northward propagation of Rossby wave packets from the western Pacific subtropical anomaly center, via the East Asian mid-latitude anomaly center, to the northeastern Asian anomaly center is apparent only in the negative event and in the lower troposphere. During the mid- and late summer, the characteristic of Rossby wave activity over East Asia for the EAP teleconnection pattern on a monthly-mean time scale is basically similar to that for the EAP event on the medium-range time scale.