The invention relates to a phase difference principle based power distribution network differential protection method. Current and voltage signals at each load switch are acquired; a phase difference of currents corresponding to two adjacent load switches is calculated, wherein at least one of the two adjacent load switches meets a condition that delta I phi max>n.delta IT+delta Idz; and if the phase difference of the currents corresponding to certain two adjacent load switches is greater than a set threshold value, then a section between the two adjacent load switches is a fault section, and the two adjacent load switches are tripped off. According to the method, only the phase difference of the currents at the two adjacent load switches needs to be calculated; fault determination is realized according to the condition met by the phase difference; the method has low requirement on data synchronization; the fault determination can be performed according to acquired information; the time required for the whole determination process is very short; the protection action speed is high; and the problem of low action speed in an existing relay protection method for a power distribution network is solved.