Nanoscale　zero-valent　iron　(nZVI)　has　received　more　attention　due　to　its　high　reactivity　in　removing　contaminants.　However,　assessing　reactivity　requires　time　and　cost　savings　to　improve　the　potential　applicability　of　nZVI.　In　this　study,　a　model　for　Cr(VI)　removal　by　nZVI　was　established　to　simulate　the　changes　of　various　ions　during　the　reaction.　The　aim　was　to　elucidate　the　reduction　mechanism　and　provide　a　new　method　for　calculating　electron　efficiency.　And　we　calibrated　the　parameters　through　experimental　data　and　characterization　analysis,　which　improved　the　reliability　of　the　model.　In　addition,　we　discussed　the　specific　effects　of　the　initial　concentration　and　initial　pH　of　Cr(VI)　on　electron　efficiency　and　reactivity.　The　results　indicated　that　the　initial　concentration　and　initial　pH　primarily　affected　the　electron　efficiency　by　altering　the　utilization　efficiency　of　active　sites　and　the　corrosion　degree　of　nZVI.　At　pH　values　of　3,　5,　7,　9,　and　11,　the　electron　efficiencies　were　39.18%,　47.56%,　58.81%,　59.12%,　and　84.19%,　respectively.　We　found　that　both　nZVI　and　Fe(II)　had　reduction　effects,　but　which　one　played　the　major　role　depended　on　the　reaction　conditions.　Finally,　the　possible　reaction　mechanisms　were　analyzed　by　combining　experiments,　models,　and　characterizations.　The　whole　reaction　process　was　divided　into　three　stages:　pollutant　adsorption,　electron　transfer　process,　and　mass　transfer　process.　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer　Nature　B.V.