The transient overreach phenomenon greatly reduces the sensitivity of zone one distance relaying protection， especially in a HV and even UHV power network. This paper proposes an algorithm for modifying the unbalanced components in a differential equation by using the quadratic function due to the difference in the transient responses from the voltage and current transformer. This algorithm is capable of preventing the phenomenon of transient overreach and markedly enhancing the tripping speed of zone one distance protection. The simulation results of dynamic experiment and real protection record show that the transient overreach can be eliminated and the performance of distance relay will be apparently improved by the proposed algorithm.