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The Northeast Cold Vortex (NECV) Is an Important weather system in the middle and high latitudes In East Asia. Its time scale is synoptic, yet the frequent activities of NECV have significant "climate effect" which influences not only the monthly temperature In the lower troposphere in Northeast China but also the Melyu rainfall in East Asia. On the basis of ERA-40 reanalysis data provided by ECMWF, the "climate effect" of NECV and Its relationship with Melyu in East Asia are studied. It Is shown that there Is significant correlation between NECV during the Melyu period and rainfall amount: strong NECV corresponds to more Melyu rainfall and weak NECV corresponds to less rainfall. In strong NECV years, the dry and cold air from the north is led to the south by NECV, converges with the lower-level warm and wet southwesterly on the north verge of Meiyu region, thus forms an unstable stratification of "upper dryness and lower wetness". Triggered by ascending motion, the Melyu rainfall amount Is more than usual. It Is on the contrary In weak NECV years. The anomalous SST in north Pacific in the previous year may be a factor that results In the anomalous NECV at Melyu period. The land-sea thermal contrast In summer facilitates NECV, while that in winter inhibits NECV. All of the above provide a meaningful result for the short-term climate prediction of NECV and Melyu. [ABSTRACT FROM AUTHOR]