There exists a false tripping risk in the traveling wave protection on UHVDC transmission lines under thunder strike,and simply increasing the set value may cause an action failure when high resistance earthing happens.In order to solve these problems,a probability model to analyze how the traveling wave protection falsely trips on UHVDC transmission lines under thunder strike,is constructed by using the parameters including the thunderbolt rate on transmission lines,the shield failure rate,the distribution probability of wave fronts and the false tripping section of traveling wave protection on the basis of thunder strike location.Then,malfunction probability is calculated on the basis of superposition principle,and malfunction frequency is obtained from the data of lightning activity.Furthermore,by adopting the two indicators,the risk assessment of the false tripping is performed.Finally,by taking a UHVDC transmission line of China Southern Power Grid as an example,the proposed method is verified by using both actual parameters and wave recording data,finding that the results accord well with the practical engineering statistics ones.