The DC loop resonance is analyzed in this paper in consideration of harmonic transfer characteristic on both sides of AC/DC and distribution parameters of long overhead DC line. Based on the characteristics of harmonic transfer between AC and DC of the equivalent converter of controlled source, the DC side equivalent impedance of the converter is derived by taking the example of single pole earth return mode. What’s more, aiming at the suppressing measures of DC blocking filter, the influences of elements parameters and arrangement modes on DC loop impedance are analyzed. It is proved that the cross layout of blocking filters in neutral bus will have an evident suppression effect on 50 Hz/100 Hz DC loop resonance. It is also recommended that blocking filters should be based on reactor and capacitor, and the variation range of reactor and capacitor parameters should be limited. Detailed DC loop model and DC simulation model on PSCAD/EMTDC are built. By combining impedance frequency characteristic scanning and time domain simulation, the above effects are simulated and verified, which provides reference for the research on DC loop resonance of long-distance UHVDC transmission.