To improve the current-carrying performance of the open-type GW4 isolating switches during normal operation and enhance the reliability of opening and closing operations during energization and de-energization，a fault diagnosis device based on multi-state parameter sensing is developed.The device takes a multi-state parameter information display system as the core and uses maintenance standard values as reference benchmarks.Practical application results show that the device can accurately measure the contact pressure of contact fingers and the closing offset distance，providing maintenance personnel with precise state parameters and fault location information.Its effectiveness and practicality have been reliably verified through both experimental testing and on-site operation.