On April16th，2012，in Gaopo converter station，the sympathetic inrush current emerged when pole2converter transformers were charged lead the blocked pole1bridge differential protection stage2（87CBY-2）misoperation，pole1turned to standby state from blocked state.This protection misoperation incident is analyzed.The mechanism on how the sympathetic inrush current was generated is studied from the point of view of the flux.The characteristics of the sympathetic inrush current and the factors that affect the size of the sympathetic inrush current are studied too.The phenomenon that the directions of three-phase sympathetic inrush currents are inconsistent is analyzed through the closing phase angle.The generation of sympathetic inrush current and the serious saturation of converter transformer（CT）caused by the aperiodic component of sympathetic inrush current that decays slowly are the reasons of the bridge differential protection malfunction.The sympathetic inrush current and the phenomenon that the directions of three-phase sympathetic inrush currents are inconsistent are simulated using PSCAD/EMTDC simulation software.Consistent results are obtained which matched the theoretical analysis.For the affect that the sympathetic inrush current impacts on high voltage direct current（HVDC）system protection，corresponding measures are proposed and verified by the Gao-Zhao DC real-time simulation system（RTDS）.The findings of this research provide valuable reference for the DC transmission project implementation as well as its security and stability enhancement.