This　work　reports　the　dehydrated　Zr-based　MOF　UiO-66(SH)(2)　as　a　visible-light-driven　photocatalyst　to　mimic　the　biological　N-2　fixation　process.　The　N-15(2)　and　other　control　experiments　demonstrated　that　the　new　photocatalyst　is　highly　efficient　in　converting　N-2　to　ammonia.　In-situ　TGA,　XPS,　and　EXAFS　as　well　as　first-principles　simulations　were　used　to　demonstrate　the　role　of　the　thermal　treatment　and　the　changes　of　the　local　structures　around　Zr　due　to　the　dehydration.　It　was　shown　that　the　dehydration　opened　a　gate　for　the　entry　of　N-2　molecules　into　the　[Zr6O6]　cluster　where　the　strong　N　equivalent　to　N　bond　was　broken　stepwise　by　mu-N-Zr　type　interactions　driven　by　the　photoelectrons　aided　by　the　protonation.　This　mechanism　was　discussed　in　comparison　with　the　Lowe-Thorneley　mechanism　proposed　for　the　MoFe　nitrogenase,　and　with　emphasis　on　the　[Zr6O6]　cluster　effect　and　the　leading　role　of　photoelectrons　over　the　protonation.　The　results　shed　new　light　on　understanding　the　catalytic　mechanism　of　biological　N-2　fixation　and　open　a　new　way　to　fix　N-2　under　mild　conditions.