When the rear high-voltage DC/DC converter of on-board charger in the electric vehicle is started， the inrush current is large and the soft start control algorithm is too complex. Therefore， it is proposed to integrate the rear high-voltage output DC/DC converter of the charging module with the low-voltage output bidirectional DC/DC converter， sharing high voltage capacitors，control board and auxiliary power supply. A new segmented soft start control strategy is proposed first time that the high voltage capacitors are reversely pre-charged by the low voltage battery using bidirectional DC/DC converter. A software simulation and an experiment of 6.6 kW module were built. The results show that the strategy can limit the large inrush current and reduce startup times. What’s more， it was very simple to implement. Some hardware circuits are omitted which can help reduce the volumes， weights and costs of module. It has good application prospects and promotion values.