To improve the preprocessing quality of the Shandong geomagnetic network data which were disturbed by High Voltage Direct Current(HVDC)transmission,we summarized and analyzed the preprocessing condition of the Shandong Geomagnetic Network during the disturbance by the Ningdong HVDC transmission over the years. The relative difference detection function and preprocessing function of National Earthquake Precursor Data Processing System is applied. The result shows that the Ningdong HVDC transmission disturbances are generally removed after the data preprocessing. Meanwhile,there are still some problems,such as misjudge of the HVDC transmission disturbance,misjudge of the beginning and ending time of the disturbance,inaccuracy preprocess of the disturbance magnitude,etc. Corresponding solutions are proposed to the specific problems,such as the double-check of the data,slowly varying step function to reprocess,and reinforced research to disturbance characteristic of H and D.