Abstract: Warm fronts are one of the important weather systems in Northeast China, and their activities are closely related to important weather events such as strong winds and precipitation in winter half-year. However, due to the lack of high-precision and long-term warm front datasets, long-term climatological studies on warm front activities in this region remain relatively limited. Using ERA-5 reanalysis data from 1979 to 2021, this study obtains a 43-year dataset of warm front activities based on an automatic warm front identification method using the Detection Transformer (DETR) deep learning model. The reliability of this method is verified by comparing it with manual analysis and traditional objective methods. Based on this dataset, the characteristics of warm front activities in Northeast China during the winter half-year and the possible causes of its anomalies are investigated. The results indicate that Northeast China is one of the regions with the highest frequency and strongest activity of warm fronts in winter half-year on the East Asian continent. The intensity of warm front activities exhibits significant interannual variability, featuring a variation period of 2—3 years. Composite analysis shows that in the years of strong warm front activities in Northeast China, the East Atlantic/West Russia (EATL/WRUS) teleconnection pattern over Eurasia exhibits a distinct negative phase and negative geopotential height anomalies appear at 500 hPa over Northeast China. It indicates a deepened East Asian trough, accompanied by an intensified upper-level jet stream and enhanced atmospheric baroclinicity. Furthermore, it is found that the warm front activity anomalies in Northeast China are closely related to the North Atlantic Tripole (NAT) mode. Combined with wave activity flux diagnostics and Linear Baroclinic Model (LBM) sensitive experiments, it is shown that sea surface temperature (SST) anomalies in the middle and low latitudes of the NAT mode trigger a Rossby wave train in the mid-to-upper troposphere. This wave train propagates eastward from Europe, passes over the Caspian Sea, and reaches Northeast China, thereby affecting the intensity of warm front activities in Northeast China.