A　natural　circulation　small　modular　reactor　(NCSMR)　is　designed　and　the　severe　accident　of　the　NCSMR　was　analyzed　with　MELCOR　code　in　this　work.　The　NCSMR　is　a　330　MWt　light　water　reactor　no　reactor　coolant　pumps　and　no　active　safety　injection　systems　similar　to　the　design　of　NuScale　reactor.　A　MELCOR　code　model　was　developed　for　the　reactor.　The　MELCOR　model　shows　consistent　results　in　steady　state　operation　with　the　design　values.　The　NCSMR　severe　accident　analyzed　in　this　work　was　induced　by　the　small　break　loss　of　coolant　accident　in　the　reactor　pressure　vessel　and　a　crack　in　the　containment　pool　wall.　The　decay　heat　removal　system　is　assumed　to　fail　for　the　main　steam　line　break.　The　results　indicated　that　the　RPV　pressure　decreases　quickly　while　the　containment　pressure　increases　followed　by　the　opening　of　reactor　vent　valves.　The　core　exposes　and　heat　up　with　the　coolant　leakage　and　finally　collapsed　to　the　lower　plenum,　leading　to　the　lower　head　breach.　High　temperature　core　corium　quickly　broke　the　relatively　thin　containment　vessel　wall,　and　was　discharged　to　the　containment　pool　floor,　leading　to　the　molten　corium　concrete　interaction.　The　fission　products　release　during　the　accident　process　was　also　analyzed.　The　severe　accident　sequence　shows　that　the　NCSMR　has　much　longer　time　duration　for　the　reactor　vessel　lower　head　failure　to　occur　compared　to　conventional　commercial　nuclear　power　plant　under　severe　accident　conditions.　The　analysis　results　help　identify　appropriate　accident　management　strategies　and　countermeasures　for　the　potential　extreme　natural　hazard　induced　severe　accidents　in　NCSMR.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.