Abstract: In the 10 kV AC distribution network, KYN28-12 high-voltage switchgear is widely used and has a large inventory. Closing failures of high-voltage switchgear are a high-frequency fault in operation and maintenance. Such failures caused by its secondary control circuit (accounting for about 50%) are difficult to eliminate due to the complex circuit principle. This article takes the KYN28-12 switchgear equipped with VS1-12 handcart circuit breakers as an example, and uses a combination of schematic diagrams and physical diagrams to analyze in detail the composition principle of the secondary control circuit. Based on this, it analyzes the causes of closing failures caused by the secondary circuit and clearly expresses them in the form of a fault tree. It also proposes targeted disposal methods and steps, which are simplified and solidified in the form of a flowchart to provide technical guidance for operation and maintenance personnel.