The Northeast Cold Vortex (NECV) is a major synoptic system that causes chilling damage, sustained rainfall and sudden severe convective storms over Northeast China. By using the National Centers of Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data and high resolution gridded precipitation data over China provided by the Chinese Academy of Meteorological Sciences, an objective index of the NECV (NECVI) is defined, and then the characteristics of the northeast cold vortex activities on intraseasonal timescale and its relationship with the circulation and rainfall are investigated. Results show that the activities of the NECV exhibit remarkable 10-30-day oscillation. The 10-30-day oscillation of atmosphere circulation associated with the NECV activities obviously locks with the precipitation anomalies over eastern China, and modulates the locations of anomalous rain belts. The anomalous rain belts over eastern China shift from north to south along with the northwest-southeast movements of the NECV and associated low frequency circulation. Moreover, the relationship between the 10-30-day activities of the NECV and the atmospheric teleconnection patterns in mid-high latitudes is discussed. The low frequency circulation associated with the NECV is one part of the Eurasian (EU) pattern teleconection-like wave train in summer. The EU wave train converges with the East Asian-Pacific (EAP) pattern teleconnetion-like wave train in eastern Asia. The interaction between them affects the velocity and direction of low frequency system related with the NECV, and further determines the location and duration of precipitation over eastern China. Therefore, the preceding development of the low frequency wave trains of EU pattern and EAP pattern might indicate the following stage of rainfall over eastern China. This study will provide a reference for the 10-30-day extended-range weather forecast of severe precipitation over eastern China.