Carrier transport through an n-type semiconductor grain boundary with a double Mott barrier consisting carrier depletion layers,acceptor defect layers (ACLs) on grain surface and negative-charged interface by trapping of majority carriers is studied.The effect of ACL on the barrier,current,nonlinearity and capacitance is especially treated.The change of barrier under bias governs transport properties,and ascertains the existance of pre-breakdown,breakdown and upturn regions.ACLs result in a change of barrier and its intensifying decline under bias,and thus enhance the current change and nonlinearity,and largely determine the leakage current.And ACLs reduce capacitance at high frequency by broaden barrier but increase capacitance peak originated from the resonant response of interface charge under bias.