Abstract: The insulation fault of “JIAOLONG” manned submersible during its experimental application stage is introduced. Based on the insulation detection equipment of “JIAOLONG” manned submersible, we develop an insulation fault detection system using MCGS embedded virtual instrument technology to acquire the grounding detection data and deal with them in real time, which greatly improves the accuracy and efficiency of the insulation detection and provides the most effective assistant for the pilot to detect and find the underwater ground fault in real time. With good application prospect and development potential, this technology can be widely used in the field of insulation grounding detection of underwater vehicles.