Abstract: The method based on the Deutsch assumption iswidely used to calculate the ionized field under HVDCtransmission lines when there are not buildings nearby. But theexistence of the buildings will influence the ionized fieldgenerated by the HVDC transmission lines,so it’s necessary toknow that whether the method based on the Deutschassumption can be still used in this situation. Based on theDeutsch assumption,a method to analyze the ionized fieldunder HVDC transmission lines with buildings nearby isproposed. First,the Optimized Charge Simulation Method wasused to calculate the space-charge-free electric field. Then theionized field around the buildings was calculated based on theDeutsch assumption. Finally,We measured and calculated theionized field on the ground surface and the top of the buildingmodel when there was a building model placed near the DCexperimental line sections. The calculation results anddistribution regularities of the ionized field on the groundsurface and the top of the building model computed by themethod basically agree with the experimental measutementresults. This indicates that the method based on the Deutschassumption is still applicable. The method can be used tocalculate the ionized fields under the HVDC transmission lineswith various buildings nearby.