All the ships contain different metals, these metals in seawater has a different potential, soak a long time will corrupt slowly, that will affect the ship's life. In order to eliminate corrosion, we need to insulate the different metals, so that there is no corrosion current loop between them. In this paper, we developed a new type of insulation testing equipment to detect insulation for this situation. The equipment, using voltage measurement and resistance measurement for dual diagnosis, determine the degree of insulation. After the successful development of this device, a series of tests was done, get good results.