The invention discloses an extra-high voltage long-distance DC line protection algorithm based on new energy grid connection. The algorithm mainly comprises the following steps: obtaining electrical sampling data obtained after sampling of each electrode of the two sides of a protected DC transmission line, and carrying out initial judgment on practical operation state of the line in real time; according to the state obtained after initial judgment, starting an integral-form longitudinal impedance time domain protection algorithm; and when the DC transmission line drives time domain increment of the corresponding detected current above to be able to be measured effectively due to fault, starting a set longitudinal impedance algorithm and determining whether the line has an internal fault according to the time domain integral result of longitudinal impedance. Through a novel extra/ultrahigh-voltage DC transmission line unit protection algorithm, high-frequency harmonic interference hard to be resisted in an existing current differential protection algorithm configured to the DC transmission line can be eliminated effectively, influence due to ultra-long-distance line distribution parameters is eliminated, and meanwhile, setting time of tripping action is obviously reduced.