Lockdown　measures　have　been　widely　used　to　control　and　prevent　virus　transmission　in　pandemic　regions.　However,　the　psychological　effects　of　lockdown　measures　have　been　neglected,　and　the　related　theoretical　research　lags　behind　the　practice.　The　present　study　aimed　to　better　understand　the　mechanism　of　social　anxiety　in　pandemic　regions　where　the　lockdown　measures　were　imposed,　based　on　the　conceptual　framework　of　the　Stimulus-Organism-Response　(SOR).　For　that,　this　research　investigated　how　lockdown　measures　and　psychological　distance　influenced　social　anxiety　in　the　pandemic　region.　The　Chinese　national　data　was　analyzed　for　the　outcome.　The　results　showed　that　(1)　psychological　distance　mediated　the　relationship　between　pandemic　COVID-19　severity　and　social　anxiety,　(2)　lockdown　measures　buffered　the　detrimental　effect　of　the　COVID-19　pandemic　severity　on　social　anxiety,　(3)　lockdown　measures　moderated　the　mediation　effect　of　psychological　distancing　on　social　anxiety　caused　by　the　COVID-19　pandemic.　In　conclusion,　under　the　SOR　framework,　the　lockdown　measures　had　a　buffer　effect　on　social　anxiety　in　pandemic　regions,　with　the　mediating　role　of　psychological　distancing.　©　2020　by　the　authors.　Licensee　MDPI,　Basel,　Switzerland.