Abstract: Extreme cyclones entering the Arctic from the mid-high latitude North Atlantic can cause anomalous warming in the Arctic region, which is closely related to extreme weather in mid-high latitudes and is very harmful. However, there are few studies on the impact of extreme cyclones upon weather and climate in China. Physical processes and mechanisms of two extreme cyclones (C1 and C2) affecting cold spells in China during January and February of 2015 are explored, ERA-Interim reanalysis data and observations from China meteorological stations are used. Results show that extreme cyclones occur on the mid-high latitude North Atlantic and meanwhile the anomalous warming appears near the extreme cyclones center in the lower and upper atmosphere. When extreme cyclones move northward, circulations in mid-high latitudes are shown as the formation and maintenance of Ural Blocking and the break-up of the polar vortex. Then the mid-high latitude trough deepens and moves southward over China, and the cold air intrudes southward into China driven by the northerly flow behind the trough, which results in cold weather occurring in China. Furthermore, the mechanism of the apparent adjustment in the polar vortex and general circulation are explored. It shows that the anomalous warming accompanied by extreme cyclones promotes the development of the mid-high latitude troughs and ridges through the energy dispersion of anomalous Rossby waves. In addition, comparison analysis in terms of their occurrence and track shows that there are significant differences between C1 and C2. Compared with C2, C1 occurs in higher latitudes and has an eastward track. Because of these differences, anomalous Rossby waves of C1 are divided into two branches which disperse energy upstream along high latitude and middle latitude, but C2 only has one branch of the anomalous Rossby wave dispersing upstream along the mid-latitude westerlies. Due to the discrepancy of anomalous Rossby waves between C1 and C2, adjustments of circulation in two events are different. Affected by these factors, C1 corresponds to a wider range of cold weather, and under effects of a little trough the duration of 5 d is longer than C2's which only lasts for 3 d. Cold spells corresponding with C2 only affects Northeast China, but apparently its intensity is slightly stronger than C1's. These results indicate that extreme cyclones are one of the important causes of cold spells in China. It also should be pointed out that more extreme cyclone events will be analyzed to draw more definite conclusions in future and provide a new reference for forecasting cold spells in China.