A　new　electrochemical　model　has　been　established　to　explain　the　carbonation　behavior　of　marine　sand　mortars.　To　conduct　the　mathematical　derivation　of　the　new　model,　a　curvilinear　equation　in　Nyquist　plot　was　acquired.　The　reliability　of　the　model　has　been　proved　by　way　of　comparing　the　new　model　with　the　previous.　The　experimental　results　demonstrate　that　electrochemical　impedance　behavior　of　mortars　has　been　moderated　in　the　process　of　the　carbonation.　The　carbonation　process　can　be　quantitatively　analyzed　by　the　parameters　fitted　from　the　electrochemical　model.　Moreover,　prediction　of　the　carbonation　depth　can　be　achieved.　©　2018,　Editorial　Department　of　Journal　of　Building　Materials.　All　right　reserved.