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The invention discloses a method for estimating loop-closing operation safety of a medium-voltage power distribution network. The method comprises the steps of acquiring a topological structure, an equipment parameter and real-time running data of a loop-closing network, and estimating a state of a high-voltage power distribution network to obtain voltage amplitude and a phase angle of a 10kV busat an initial end of a loop-closing feeder; selecting a ratio between an active power load and a reactive power load of each load point on the loop-closing feeder and a ratio between an active power and a reactive power of the initial end of the feeder as input variables, and calculating each order semi invariant of the input variables according to historical load data; performing certainty powerflow and loop-closing current calculation; calculating each order semi invariant of a loop-closing current; solving accumulation probability distribution of the loop-closing current; and calculating out-of-limit probability of each loop-closing current, and estimating safety of the loop-closing operation. By the method, the loop-closing operation safety of the medium-voltage power distribution network can be quantitatively estimated, the problem that the real-time load data of each load point in the feeder in practice cannot be acquired is solved, and the problem that a probability distribution function of the input variable is needed to be known during solving the semi variant by a traditional numerical method is also solved.