<p>In this paper, to figure out the possibility of partial discharge diagnostics for HVDC MI submarine cables, and Mass Impregnated (MI) cable model was designed, and patterns and pulse waveforms of DC PD (Direct Current Partial Discharge) until the insulation breakdown were measured and analyzed. To verify the reliability of the experiment, partial discharges of the single void model and surface discharge model were also measured for comparison. As a result, the DC PD of the MI cable model showed that the discharge magnitude continuously increased as the applied voltage increased, but the discharge frequency significantly decreased as the ratio of overlapped or consecutive pulses increased, unlike the single void model. The occurrence of overlapping or consecutive pulses was interpreted as the discharges occurring when one butt-gap discharge triggered an adjacent butt-gap discharge, thereby bridging the butt gaps. Because overlapped or consecutive pulses had long durations and low-frequency components, it is expected that partial discharge pulses propagated over long distances could be measured even at the termination of submarine cables. The PSA (Pulse Sequence Analysis) for DC PD of the MI cable model showed as a void discharge pattern similar to that of the single void model, and it is expected that it can be distinguished from the surface discharge and converter noises.</p>