Abstract: The line-commutated-converter based high voltage direct current（LCC-HVDC） transmission system has commutation failure（CF） issues, which brings threat to the security and stability of power grid. Firstly, the basic principle of the CF issue in LCC-HVDC was analyzed. Then, the existing mitigation methods were reviewed, including the control and protection approaches, the supplementary devices and the evolved converter typologies. Finally, facing the feature of complex AC/DC interconnection in power system with renewable energy sources, the prospective research interests in the area of the CF mitigation were indicated from four aspects, i.e., accurate mathematic model, complex coupling mechanism, fast prediction and judgment, and novel mitigation approaches of CF issues.