Arc reflection method（ARM） is a kind of power cable fault locating method widely used nowadays. It is difficult to choose exact time for test pulse emitting into the cable during cable fault testing and fault arcing， because the arc resistance dynamic characteristic is not clearly known. Therefore the characteristics of voltage， current of ARM fault locating device and arc resistance at fault location during the discharge process are analyzed. It proves that in period of DC arc discharge arc resistance on the fault spot is lower and stable as a whole， which maintains a relative long time and is the best period of time for pulse emitting into the tested cable. A new choosing pulse emitting time algorithm based on maximum current and arc resistance dynamic characteristic on fault spot is proposed. This method only needs to calculate variance of voltage sampling of ARM and to judge the state of fault arc resistance so as to choose a pulse emitting time. In addition， the intermittent fault can also be located without using arc prolong device. Recorded experiment data proved correctness of the proposed technique.