Abstract: The wide application of communication optical cable can significantly improve the anti-interference ability of the communication system, and the DC transmission project has the technical conditions to simplify the design of direct current filter（DCF） and improve the interference limit value. ±1100 k V UHVDC project DCF is huge and difficult to develop, which will seriously affect the technical scheme of the indoor DC Yard, and it is necessary to simplify the design. Simplified DCF design principle and step were proposed. The basic form of simplified filter was determined with the minimum resonant branch which is necessary. Based on ±1100 k V project,to limit crest value of continuous operating voltage（CCOV） of the DC circuit, the main capacitor, parallel resonant frequency, filter resistance value, filter resistance connection form were optimized. The simplified DC filter technique program was put forward for the world’s first ±1100 k V UHVD project, which reduces the main capacitance value of the DC filter, reduces the volume and occupation of the filter tower, reduces the difficulty of the equipment development, and saves the investment of the project.