In　this　paper,　a　2D　mesoscale　finite　element　(FE)　numerical　model　of　mortar,　considering　the　influence　of　the　ITZ,　was　proposed　to　evaluate　the　corrosion　of　mortar　in　sodium　sulfate.　On　the　mesoscale,　the　corroded　mortar　was　regarded　as　a　three-phase　composite　material　composed　of　sand,　cement　paste,　and　an　interface　transition　zone　(ITZ).　Firstly,　the　volume　fractions　and　mechanical　parameters　(elastic　modulus,　Poisson＇s　ratio,　and　strength)　of　the　mesoscale　phases　were　obtained.　Then,　the　cement　paste　and　the　ITZ　were　combined　to　form　an　equivalent　matrix　by　homogenization　methods,　and　the　calibrated　constitutive　relations　of　the　equivalent　matrix　were　established.　Subsequently,　a　two-dimensional　(2D)　random　circular　aggregate　(RCA)　model　and　a　2D　random　polygonal　aggregate　(RPA)　model　of　corroded　mortar　were　established　using　the　random　aggregate　model.　The　failure　process　of　corroded　mortar　specimens　under　uniaxial　compression　was　simulated　by　the　mesoscale　FE　numerical　model.　Comparing　the　simulation　results　with　the　measured　stress-strain　curves　of　the　uniaxial　compression　test,　it　was　found　that　the　simulation　results　of　the　2D　RP　model　were　closer　to　the　experimental　results　than　those　of　the　2D　RC　model.　Meanwhile,　the　numerical　simulation　results　were　in　good　agreement　with　the　experimental　results,　and　the　error　values　of　peak　stress　between　the　simulation　results　and　the　measured　results　were　within　7%,　which　showed　that　the　2D　mesoscale　FE　model　could　accurately　predict　the　results　of　a　uniaxial　compression　test　of　a　mortar　specimen　under　sulfate　attack.