The invention relates to a method and a device for protecting lines of a time blind area. The method comprises the following steps: obtaining busbar differential protection information as well as current data of other elements and lines on busbars from a process layer network; when CT broken lines are judged, calculating the vector sum of each element and line participating busbar differential calculation to be zero, calculating the phase and amplitude of interval three-phase current; enabling the calculated phase and amplitude of the interval three-phase current to participate protection logic calculation, and outputting protection action information according to calculation results. By using the advantages, such as data transmission digitization, networking and information sharing, of an intelligent substation, data self-healing is realized in the time blind area for accident handling of operation and maintenance workers, and an override trip risk caused by protection function loss is eliminated.