Disclosed are a method and device for processing a voltage drop, a grid interconnection method and device for processing an electrical apparatus, and a system. The method includes: acquiring a drop amplitude of a first voltage for each phase in a three-phase alternating current (S204); and under a condition in which the first voltage for any phase in the three-phase alternating current drops, performing reactive power compensation according to a drop amplitude of the first voltage for a phase in which the first voltage drops (S206). Therefore, the electrical apparatus has a low voltage ride-through function, thereby solving the technical problem of a large deviation of voltage drop amplitude determination arising from an asymmetrical drop of three phases.