To improve the capability of countermeasure during detecting electric field of ship, basic method of detecting electric field is analysed, and the mathematical model of electric field of ship and electrod sweep are established in the three-layers media(air-seawater-seabed), then the main problem during electric field detection is pointed out after contrast and analyse. Based on the character of gradient of electric field distribution, the method of improving capability of detection is put forward, and the calculation is done. The results of calculation prove that the method can obviously improve the characteristic of countermeasure during detecting electric field of ship, and increase detecting range.