Under the background of the operation of ultra-high voltage DC transmission line, the phenomenon of current transformer (CT) saturation caused by DC bias is becoming more and more serious, and it is urgent to suppress CT saturation. In this paper, through the establishment of DC bias generation mechanism and CT equivalent model, the secondary current and iron core magnetic chain expressions of three CT transient saturations are derived, and the CT transient saturation caused by DC bias is suppressed based on DC compensation method. Based on the PSCAD（Power Systems Computer Aided Design） simulation platform, the influence of DC bias on CT secondary current is analyzed, and the correspondence between DC and bias current is compensated by quantitative calculation. Suppressing the transient saturation of the current transformer can ensure that it accurately changes the current flow to the secondary side, the secondary current waveform will not be distorted, can avoid the protection error caused by the poor current is too large, and ensure the safe and reliable operation of the power system.In addition, for CT saturation caused by excitation surge and ground fault, the simulation results verify that the method is feasible.