Abstract: To understand energy transfer during sudden stratospheric warming (SSW) events in the middle atmosphere, the 2023 SSW is studied by using the analysis tools of the multiscale window transform (MWT) and MWT-based localized energetics analysis and theory of canonical transfer (MS-ECT). The energy transfer in the mesosphere is diagnosed and compared with that in the stratosphere. The energy fields are first reconstructed onto three scale windows: a large-scale window, an SSW-scale window, and a synoptic-scale window. Results showed that the work done by pressure (pressure flux) plays a critical role in coupling the mesosphere and stratosphere during SSW events. The cross-scale energy transfer (canonical transfer) of available potential energy is always directed from the large-scale to the SSW-scale window, indicating the central role of baroclinic instability in both the stratosphere and mesosphere. Comparative analysis with the 2012–2013 SSW event revealed the consistent presence of baroclinic instability across both events. However, the 2023 event exhibited significantly stronger energy transfer magnitudes in the mesosphere. These results highlight the consistent role of baroclinic instability and pressure flux in mediating cross-scale energy transfer during SSWs, providing a clearer understanding of stratosphere–mesosphere coupling.