The invention discloses a protection method for a DG grid-connected transformer grounding system, comprising the steps of: considering DG capacity and balanced capacity on local load, and selecting a DG grid-connected transformer, namely selecting a primary winding ungrounded transformer or a primary grounded grid-connected transformer winding; choosing the primary grounded grid-connected transformer winding, when system zero-sequence protection sensitivity is reduced through a protection constant value verification to cause the situation that the faults at the tail end of a feeder line cannot be correctly judged, additionally installing a recloser on the grid-connected transformer; and when the primary winding ungrounded transformer is selected, adopting a way of zero-sequence overvoltage warning. By analyzing the induction overvoltage problem caused after introducing the DG, and the matching problem in system protection matching relations, different modes of connection of the grid-connected transformer winding, and corresponding protection schemes are proposed for different DG access conditions; and in facing the condition that the current distribution network protection typical design is not specific to the high degree of permeability of DG access, new effective thoughts and solutions for protection configuration for the DG access are provided by the protection method.