Abstract: The paper introduced design principle of interlocking device of switchgears and pointed out that the interlocking device should be designed in accordance with requirements of “Five Prevention” and should have integrity and reliability. It analyzed problems existed in interlocking of back door of switchgears, switchgears without grounding switch and front and underside door of switchgears, made improved designs, analyzed conflict problems of operating procedure and interlocking device, and proposed a solution. The functions of improved interlocking device of KYN44-12 switchgear are more complete and reliable, the design is more reasonable, and the improved device can fully meet the requirements of “Five Prevention”.