The Northeast Cold Vortex (NECV) is a major synoptic system at the mid and high latitudes of East Asia,of which the frequent activities may lead to significant impact on climate change,not just in Northeast China,but in the Haihe River Basin ( HRB). In this paper,an objective index of the NECV (NECVI) is defined,and then a significant correlation between the activities of the NECV and precipitation in the HRB is investigated during early summer,by using daily precipitation data of 34 meteorological stations over the HRB and NCEP/NCAR reanalysis data. Results show that frequent (infrequent) activities of the NECV are related to more (less) precipitation in the northern basin,corresponding to the spatial characteristic of precipitation in the HRB,with more (less) in north and less (more) in south,when the second EOF mode time coefficient is positive (negative). During early summer,the frequent activities of the NECV are often related to the cold air moving southward,the intensive moisture convergence,the unstable stratification occurring and strong ascending movements developing in the low troposphere in the northern basin,which offer necessary atmospheric circulation conditions for increasing of precipitation,and vice versa. The symbol consistency in recent three decades between the NECVI and precipitation anomalies in the lower reaches of the HRB is up to 83%. In conclusion,a reference is offered for precipitation prediction in the HRB,especially the lower reaches during early summer.