Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused a global pandemic and a serious impact on human life and health. The spread of this virus, coupled with the emergence of many mutants, has posed increasingly formidable challenges to the design and development of antiviral drugs. Recently, it has been discovered that dalbavancin can bind to angiotensin-converting enzyme 2 (ACE2) of host cells with high affinity, blocking the interaction between the spike protein and ACE2, thereby making it a potentially promising anti-SARS-CoV-2 drug. It's necessary to use molecular dynamics (MD) simulations and binding free energy calculations to explore the source of the high binding affinity of dalbavancin. Computation analysis showed that due to the large molecular structure of dalbavancin, it exhibits stronger van der Waals (vdW) interactions with ACE2, which enhances the total binding free energy. In addition, our study has identified the hot-spot residues, among which the residue Lys353 has the most significant contribution, providing one-third of the total binding free energy. The energy of Lys353 was also dominated by vdW interaction. These results and analysis may provide constructive insights and suggestions for the design and development of anti-SARS-CoV-2 drugs, thereby advancing the progress in viral treatment.