Based on an introduction of normal±500 kV HVDC system protections in bi-pole area， this paper proposes some new protection principles and actions， which include a criterion of differential current between bi-pole under bi-pole operation mode and an action of switching to metallic return mode under mono-pole operation mode， in the bi-pole area of±800 kV ultra HVDC system. It makes the ultra HVDC system continue to operate with fault and harmless for equipment and decreases a probability of bi-pole block caused by actions of bi-pole protections.