Abstract: Using the ERA40/ERA-interim daily-mean reanalysis data and the daily station data from National Climate Center, this study explores the stratosphere-troposphere interaction processes during nationwide Extensive and Persistent Extreme Cold Events (EPECEs). The results show that nationwide EPECEs usually experience three stages: (1) Cold air accumulation in Urals-Siberia area, (2) cold outbreak, and (3) cold-decay, which corresponds respectively to the formation, the development and the collapse of the Urals-Siberia tilted ridge in the middle troposphere, as well as the recovering, the persistence and the re-weakening of the stratospheric polar vortex. Firstly, a wavenumber-2-type anomaly pattern, mainly dominated by disturbances in Atlantic, appears in the extratropical troposphere and propagates upwards to weaken the stratospheric polar vortex. Subsequently, when the wavenumber-2-type anomaly pattern changes to a wavenumber-1-type in the stratosphere, wave propagation turns to downward while the stratospheric polar vortex recovers its strength. Followed is a wavenumber-1-type anomaly pattern in the troposphere with its positive pole centered in the eastern Europe which helps the establishment of a Ural blocking and accumulation of cold air from the Arctic Ocean in front of the blocking. Thereafter, with the eastward shifting of the positive pole of the wavenumber-1-type anomaly pattern to central Siberia, a large-scale tilted ridge arching across the Siberia is established. The cold-air accumulation area thus also moves eastward to central Siberia. Before the cold-air outbreak, a trench structure is formed by the large-scale transversal trough downstream of the ridge and an upstream short-wave trough. Cold air outbreaks into China as the transversal trough quickly turns into a vertical form. Meanwhile, the stratospheric polar vortex weakens again due to the enhanced upward wave propagation related to the persisting large-scale tilted ridge in the troposphere. Finally, with the collapsing of the blocking and troughs, meridional transport of cold air diminishes and EPECEs decays.