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In the context of global warming, abrupt transitions between extreme temperature states (extreme temperature variability events) pose severe threats to both ecosystems and socioeconomic systems. However, previous studies have primarily focused on the regulatory effects of atmospheric intraseasonal oscillation (ISO) on extreme temperatures from the perspective of a single scale, leaving the synergistic driving mechanisms of multi-scale ISO on extreme temperature variability poorly understood. This study investigates the synergistic influence mechanisms of 10–30-day and 30–60-day ISO on extreme temperature variability events in eastern China. Utilizing ERA5 reanalysis data from 1979 to 2024, the record-breaking extreme winter of 2023–2024 is employed as a representative case study to systematically elucidate these mechanisms. The results indicate that the winter of 2023–2024 was marked by a record-high surface air temperature variance, accompanied by two prominent extreme temperature variation processes. Wavelet and empirical orthogonal function (EOF) analyses reveal that both ISOs were anomalously strong during this winter and exhibited significant positive correlations with temperature variance, with the 10–30-day ISO playing a more dominant role. Phase evolution analysis demonstrates that phase-locking between the leading 10–30-day modes precedes extreme temperature events by approximately 5 days, whereas the 30–60-day ISO modulates the monthly-scale persistent warm or cold backgrounds. Dynamic diagnosis shows that the ISO-related wave activity flux drives the evolution of key circulation systems, such as the Ural blocking high and the East Asian trough, thereby governing the abrupt temperature reversals. Thermodynamic budget analysis highlights the dominant role of diabatic heating, particularly in the northern key region, where its 10–30-day component is crucial for rapid temperature reversals. Critically, a synergistic effect significantly amplifies the intensity and frequency of extreme temperature variations when both ISOs are in positive phases concurrently. This study advances the understanding of the multi-scale dynamical mechanisms underlying extreme temperature variability and provides a scientific foundation for the extended-range forecasting of such events. Moreover, the findings offer critical insights for enhancing regional climate resilience and informing risk mitigation strategies for major urban clusters in eastern China.