Magnetizing inrush current will occur when the transformer is energized without load, which will cause that the already energized neighboring transformers generate sympathetic inrush current. The currents have influence on the operation of HVDC system if they occur in the converter transformers due to their characteristics. In this paper, the inrush current generating mechanism is discussed firstly. Then the model of HVDC system is constructed in PSCAD/EMTDC based on the planned Shanxi-Jiangsu HVDC transmission system. After that, a process simulation, where one pole of HVDC system is in operation while the other pole's transformers are put into operation, is carried out. In this process, this paper studies the influence of fairly large inrush current on the operation of HVDC system. The simulation result shows that the inrush current and sympathetic inrush during energization of the converter transformers cause the fluctuation of operation of HVDC system.