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The robust negative correlation between the Siberian High (SH) intensity and winter surface air temperature (SAT) in Northeast China has been widely used for winter climate seasonal forecasting. However, this traditional viewpoint varies when considering the changes in SH spatial extension during boreal winter. Here, a newly defined SH index representing both SH intensity and spatial extension shows two distinct influences of a stronger SH on the SAT in Northeast China. The stronger SH with a decreasing eastern edge, which features a meridional see-saw dipole of abnormal circulations centred over the Arctic and Siberia, respectively, results in a warmer winter over Northeast China. In this situation, the decreasing SH is linked to the enhanced Arctic Polar vortex through a tropospheric-stratospheric interaction. However, a stronger SH with an expanding eastern edge is coupled with the East Asian trough (EAT) and results in a colder winter in Northeast China. The SH and EAT anomalies are embedded in a zonally oriented wave-train originating from the North Atlantic in the troposphere. Because of the diversity of impacts, the SH intensity and zonal extension should be jointly considered for seasonal forecasting of winter SAT anomalies in Northeast China.