A novel disturbance identification method for HVDC transmission line main protection is proposed in this paper in order to prevent the mal-operation of protection caused by disturbance. The identification principle is based on the different variation trends of voltage in the cases of disturbance and fault, and this characteristic difference of voltage will be amplified in the IMF with the lowest frequency band by decomposing the voltage fault component using EMD. Thus, integration value of the selected IMF is employed as the criterion for distinguishing disturbance from fault. A ±500kV HVDC system simulation model, including detailed lightning stroke simulation model, is built in PSCAD/EMTDC. Simulation results show that the proposed disturbance identification method can distinguish disturbances from faults correctly with ultra-high-speed, providing a strong guarantee for main protection to prevent the mal-operation in the case of disturbance.