The present research theoretically studes the forces and motion characteristics of the water droplets. The solution of the differential equation expressing the velocity of the water droplet is given. The influence mechanism of frequency on separation performance under the electromagnetic coupling field was explored experimentally. The experimental results show that the electric field and the electromagnetic coupling field were affected by the change of frequency simultaneously, and the separation efficiency was changed under the combined action of them. Within 500Hz, when the frequency is higher than the turning frequency, the separation efficiency of emulsion treated by the electromagnetic coupling field is less affected by frequency, and the optimal frequency formula is still valid.