<p>Quasi-biweekly (QBW) variations account substantially for the intra-seasonal variability of the East Asia-Pacific (EAP) teleconnection, exerting significant impacts on East Asian summer weather. However, its year-to-year variability and underlying mechanisms remain unclear. Here we demonstrate that the activity of QBW EAP events exhibits significant interannual variability from 1979 to 2020, primarily attributed to event intensity rather than event frequency. In summers with enhanced QBW EAP events, active centers across the East Asian coast are enhanced and prolonged, forming a dipole pattern over the western North Pacific (WNP) in the lower troposphere during the events. Using reanalysis data and numerical simulations, we investigate the interannual variability of QBW EAP from the perspectives of triggering and maintenance mechanisms, revealing a notable modulation by tropical central-eastern Pacific (CEP) warming. In summers characterized by stronger QBW EAP activity, CEP warming induces a summer-mean cyclonic anomaly over the Philippine Sea and westerly anomalies over the tropical western Pacific (WP) at lower levels. These anomalies cause moisture convergence, ascending motion, and easterly vertical shear over the southern Philippine Sea, promoting convection which enhances the Rossby Wave Source, leading to more intense QBW EAP event. Besides, the cyclonic anomaly over the Philippine Sea and the anticyclonic anomaly east of Japan enhance the meridional shear of zonal wind between them, facilitating the transfer of barotropic kinetic energy from mean flow to sustain QBW EAP events. Our findings provide insights for improving subseasonal forecasts of East Asian summer weather and climate.</p>