Using a loop formed by steel cableway and water body is effective to communicate across the media, under water to above water. But this communication method is easily affected by environment and has poor communication quality. To improve the communication quality, the transmission characteristics and influence factors of electrical signals in the loop are studied. The equivalent circuit of communication channel is proposed according to the water body characteristics. Electrical signal transmission path and electric field distribution are analyzed by finite element simulation. The influence of the actual factors such as the communication distance, the depth of the electrode plate into the water, the width of the water body, the size of the electrode plate, the conductivity and the dielectric constant on the equivalent circuit parameters are simulation calculated. The results show that the communication distance, the plate size and the conductivity are the main influence factors of signal attenuation. When the communication distance and the plate size increase, the signal amplitude ratio is stable at 92. 2% and 95. 8%. A communication under water to above water long-distance can be realized fast and effectively by controlling the plate size and the signal frequency, which provides a theoretical reference for the design and optimization of underwater loop communication systems.