Based on the characteristic of high voltage direct current（HVDC） transmission system and combined the simulation results of PSCAD/EMTDC and the actual cases in Tian-Guang HVDC transmission practical project， this paper analyzes the negative impacts on HVDC transmission system caused by the inrush current and the sympathetic inrush when converter transformers of other pole are energized. The correlative techniques to avoid this problem used in Tian-Guang and Gui-Guang HVDC transmission project is introduced at the end of this paper. Research carried out in this paper is valuable for development of HVDC transmission projects in the future.