The invention discloses a transmission time mark wide area phasor differential protection method comprising the following steps: each device in a wide area differential protection scope obtains clock synchronization signals; each device obtains M sample data at equal intervals in adjacent clock synchronization signals, and marks time marks for the sample data; each device calculates time mark tn phasor X(tn); to extract and transmit phasor X(tn) and time mark tn at equal intervals according to wide area communication bandwidth resource; each device in the wide area differential protection scope receives phasors sent by other devices, and completes phasor synchronization according to the time mark; to use the phasor after synchronization to calculate a wide area differential protection difference amount; to quit differential phasor calculation at tk moment when the phasor at the tk moment is not correctly received because of communication quality, and to continuously calculate the differential phasor at tk+m moment. The transmission time mark wide area phasor differential protection method saves mass wide area communication bandwidth resource, reduces wide area differential protection engineering cost, and differential phasor of other moments can be still calculated when communication quality of any moment is bad, thus improving wide area differential protection reliability.