A complicated DC line fault of high voltage direct current（HVDC） is analyzed. During this DC line fault， the continuous lightning strikes resulted to action of several protections such as: DC line over-voltage protection， valve group differential protection， AC/DC conductor contact protection， bridge differential protection and 50 Hz protection， etc. In accordance with protection function principle of DC control concerned and fault records， a detailed analysis on the fault process is carried out. Furthermore， the improving suggestions such as: study on reason and influence of DC line over-voltage， attach importance to the coordination of thyristor valve and its control system with the DC protection， properly improve the logic of the open HSNBS， etc are put forward.