Abstract: A novel risk evaluation method is proposed in this paper for planned maintenance of HVDC transmission systems by using probabilistic method, which can quantitatively evaluate the risk of HVDC transmission system maintenance on power grid reliability. Two major indices, including the loss of load probability(LOLP) and severity index(SI), are chosen to construct the power grid operation risk indices. Based on the calculation of historical operation data and advices of dispatching department, a risk threshold criterion is proposed for evaluating planned maintenance of HVDC transmission system, below which the planned maintenance can be approved. The methodology provides an effective analysis tool for scheduling department to choose the appropriate time to arrange maintenance. Finally, by taking the China Southern Power Grid as an example, a case study is carried out, which has demonstrated the high efficiency of the proposed method.