The invention provides a method for protecting the ring main unit of a power distribution network. The method comprises the following steps: (1) collecting measuring currents and current directions at protective installation positions in the ring main unit; (2) adopting different protection configuration schemes according to the difference of protective positions inside the ring main unit, and forming protective startup information and action information; (3) forming a logic criterion according to the protective startup information and the action information to carry out fault location and determining a failure circuit breaker; and (4) accelerating protective actions according to the result of the failure location and the failure information of the circuit breaker, and quickly clearing faults. Different protection configuration methods are adopted according to different protections, and the logic criterion is formed by using the protective startup information so as to accelerate backup protective actions, so that the power failure range is effectively reduced.