Based on the analysis of the structure of DC filters, measuring point arrangement, protection system of DC filters and protection configuration strategy of protection function, the key problems in current DC filter protection of UHVDC are studied, and the corresponding suggestion and optimization scheme are given. For the protection misoperation caused by the inconsistent transient characteristics of DC filters high side and low side CT current, using the new DC filter differential protection criterion and installing optical CT measuring device in the high side and low side are suggested. Aiming at the low reliability of “selecting 2 from 3” logic export strategy caused by analog fault, a new “selecting 2 from 3” logic export strategy is proposed. The high voltage capacitor C1 internal grounding fault is simulated and analyzed by using RTDS, and a new protection function criterion and setting value suggestions are given. Study on these key problems provides a useful reference for the design of DC filter protection in the subsequent HVDC project.