The invention relates to the technical field of power system fault judgment, in particular to a transmission line time domain full-waveform protection device and a phase abrupt change amount directionjudgment method thereof. The method comprises the steps of calculating a first group of zero-sequence current instantaneous values of n+1 sampling points after the fault occurs, a second group of zero-sequence current instantaneous values of each corresponding sampling point before the set period, an abrupt change amount phase voltage of any phase and an abrupt change amount phase current of thecorresponding phase according to the sampling value information of three-phase voltage and current at the protection installation position; according to the first group of zero-sequence current instantaneous values and the second group of zero-sequence current instantaneous values, obtaining the abrupt change amount zero-sequence current; obtaining the positive sequence reactance and the positivesequence resistance according to the constraint relations among the abrupt change amount zero-sequence current, the abrupt change amount phase voltage, the abrupt change amount phase current, the positive sequence reactance and the positive sequence resistance. When the positive sequence reactance and the positive sequence resistance are less than zero, the phase has a positive fault, and the problem that the full waveform distance protection technology is not applicable to the phase-to-phase and non-grounding faults, which leads to unreliable discrimination, is solved.