Abstract: The invention relates to a parallelization method for black-start subsystems of a power grid with external support, which includes, after power blackout, partitioning the power grid into subsystems, and respectively performing black-start on the subsystems based on a power grid black-start research scheme, performing stability check on each subsystem, performing voltage calculation on parallel lines between the subsystems, checking the parallelizing simulation of the subsystems, and determining a feasible parallelizing path and a recommendable charging direction.