Abstract: The performance of a regional air-sea coupled model, comprising the Regional Integrated Environment Model System (RIEMS) and the Princeton Ocean Model (POM), in simulating the intraseasonal oscillation (ISO) of East Asian Summer Monsoon in 2003 was evaluated by comparison of the observations and results of an uncoupled model. The results showed that the regional air-sea coupled model reproduced well the spatial pattern of summer mean precipitation in 2003 and simulated a stronger ISO than the uncoupled RIEMS across eastern China, especially over the Yangtze-Huaihe Valley. Meanwhile, the coupled model showed high skill in simulating the meridional northward propagation of ISO over East Asia, and presenting the distribution and intensity of the intraseasonal precipitation and circulation anomalies over Northwest Pacific during the driest and wettest phases of the Yangtze-Huaihe Valley more realistically compared to the uncoupled RIEMS. Further analysis indicated that improvements in the simulation of ISO by the coupled model were due to better simulation of the western North Pacific Subtropical High and realistic phase relationship between the intraseasonal convection and the underlying sea surface temperature resulting from air-sea coupling.