The action characteristics of zero-sequence reactance relay are discussed.The zero-sequence reactance has the great detection ability of high resistance fault for its adaptive performance with the change in the earth fault reactance and operation characteristics，but there is a serious shortcoming of the external high resistance ground fault leading to protection maloperation at the receiving side.An improved protection scheme by adding an auxiliary mho impedance relay is proposed to solve the problem of protection maloperation under an external high resistance ground fault.Moreover，the new protection scheme also has sufficient detection ability of a high resistance fault.Theoretical analysis and simulative tests have proved the above conclusions.