The invention discloses a longitudinal zero-sequence protection method of a voltage-compensated power transmission line, and solves the problem of low zero-sequence protection sensitivity during a high-resistance grounding fault in a protection region. The longitudinal zero-sequence protection method comprises the following steps of inputting zero-sequence voltage compensation (a product of a zero-sequence current and half impedance of the whole line of the power transmission line) when a phase included angle Theta<2> between a voltage phase and a current phase of a negative sequence of one end conforms that Theta<2> is larger than 175 degrees but smaller than 325 degrees; judging whether an internal fault or an external fault occurs when the compensated zero-sequence voltage amplitude 3U<0>' is larger than 0.5V and a phase included angle Theta<0>' between the zero-sequence voltage phase and the zero-sequence current phase after compensation conforms that Theta<0>' is larger than 175 degrees but smaller than 325 degrees; and sending out an allowable trip signal to an opposite end of the power transmission line, sending out a trip command to a fuse at an end and simultaneously sending out the allowable trip signal to the opposite end when opposite end protection conforms to the abovementioned condition, so that the fuse at the end can be switched off by the fuses at the two ends when the internal fault occurs. By the longitudinal zero-sequence protection method, the problems of false action of a protection device during alternative internal fault and external fault and excessively low zero-sequence voltage due to high-resistance grounding to cause that longitudinal zero-sequence protection cannot be started are solved.