Abstract: Existing distance protection of transmission lines depends on setting calculation to avoid operation under over-load conditions.After operation of distance protection,the line load transferring to other transmission lines may result in fault expansion,so it’s necessary to find some new countermeasures to avoid the mal-operation of distance protection in post-fault over-load condition.This paper proposed a new criterion to identify between over-load and fault in voltage co-ordinate instead of that in impedance co-ordinate.In the criterion,an operation area was constructed by considering compensation voltage as operation voltage and the polarization voltage as reference voltage.The protection will operate when the operation voltage is in the operation area.In the voltage co-ordinate,the load voltage is on the line between the two power source voltages,so it’s easier for the protection to decide whether operate or not.The criterion can identify between fault and over-load radically and make distance protection avoid mal-operating after the load transferring.Its application will be benefit for the stability of power system.Simulation results show that the method is effective.