Abstract: With the global warming and the decreasing of Arctic autumn sea ice density since the onset of satellite observations, extreme cooling events in East Asia become more frequent in recent years. Based on the atmospheric circulation data such as the Arctic Oscillation Index, Arctic sea ice density and temperature, geopotential height and wind field, the causes and the spatio-temporal variations of the extreme cold waves occurred in China in January 2021 and 2024 are studied. The extreme cold waves occurred in the eastern part of China (115°00'-120°00'E, 20°00'-37°30'N) from January 1 to 9 in 2021 and from January 17 to 24 in 2024, with the lowest temperature anomalies being −9.028 °C and −7.574 °C respectively and the cooling centers being concentrated in the southern Mongolian Plateau and the northern Qinling Mountains respectively. In January 2021, the average temperature in the eastern part of China dropped to −3.8 °C, being the secondary lowest temperature record since the 21st century. According to the reanalysis data from the National Centers for Environmental Prediction (NCEP), USA, the abnormal weakening of the westerlies has made the obstruction effect of the westerlies on the cold air at high latitude weakened. When the cold waves broke out in 2021 and 2024, the cold waves located both in the high-pressure centers in Siberia and the northwest Pacific Ocean and in the low-pressure center in North China exhibited significant enhancement, which led to the cold air moving southward from Siberia, resulting in the cold wave phenomenon in the eastern part of China. The extreme cold wave in January 2024 was manifested in the first mode of the Empirical Orthogonal Function (EOF) (29.33%), while the second mode of the EOF decomposition (14.92%) indicated a cooling trend in 2021. Regression analysis demonstrates a strong correlation among the Arctic Oscillation Index, the decline in Arctic sea ice and the air temperature in the eastern part of China in January. The negative phase of the Arctic Oscillation and the decrease of the Arctic sea ice were also significant factors promoting the southward movement of the Arctic cold air. The combination of unusually strong north winds, the weakened westerly jet and the movement of the corresponding high-pressure center led to the invasion of the polar cold into the mainland of China. This is one of the main reasons for the extreme weather events in the mainland of China in January 2021 and 2024.