Electromagnetic sound sources are characterized with large output force，small size，and easy realization of ultra-low frequency output，thus they have significant advantages in unmanned mine countermeasures. The dynamic behavior of the electromagnetic sound source is affected by the coupling effect of mechanical recovery force and electromagnetic force. When the applied current exceeds the collapse current，the electromagnetic force will exceed the mechanical recovery force，and suction will occur，resulting in damage to the sound source. To accurately describe the nonlinear dynamic characteristics of the electromagnetic sound source and to evaluate the collapse current in advance，a nonlinear dynamic model of the sound source considering the dynamic magnetic leakage coefficient is established. The magnetic leakage coefficient of the air gap where the moving iron core moves to different positions is calculated by three-dimensional finite element simulation，and the dynamic magnetic leakage coefficient is obtained by fitting. The improved electromagnetic force model of the sound source is established according to the equivalent magnetic circuit method. Then，the nonlinear dynamic model of the electromagnetic sound source is established. The displacement and velocity of the sound source vibration under step excitation are calculated by Runge-Kutta algorithm，and the phase plan is drawn. The dynamic changes of phase trajectories under stable and unstable conditions are studied to provide theoretical support for designing and controlling electromagnetic sound sources.