Diagnostic analysis is made to investigate features of the moisture circulation over East Asian during the El Niño episode in northern winter, spring and autumn. It is found that in all these seasons, the anomalies of precipitation in China, atmospheric precipitable water, water vapor transport and moisture divergence over East Asia in the El Niño mature phase, differ from those in the rest of the phases. In the El Niño mature phase, positive precipitation anomalies occur in the southern part of China. More northeastward water vapor transport appears around the southeastern coast of East Asia, where moisture converges, and precipitable water is above normal, which are consistent with the precipitation anomalies. The physical process through which El Ninñ affects the East Asian climate, is also identified. Differing from the rest of the phases in the El Niño episode, the mature phase is characterized by strong convective cooling anomalies in the atmosphere, in the area (0-15°N, 110°E-150°E) over the western tropical Pacific. As a Rossby wave response of the tropical atmosphere to the cooling anomalies, an anomalous low-level anticyclone forms to the north of the maritime continent. This anticyclonic anomaly not only transports more water vapor to the area around the southeastern coast of East Asia, but also strengthens the western Pacific subtropical high, and shifts it to the south of the mainland China, which are favorable for more precipitation in the southern part of China.