CR39 detector can be used to detect the ions in laser-plasma physics experiments and to obtain information about the number, kind and energy of incident ions. Using phenomenological model, we numerically simulated the formation process of ion track in CR39 using energy loss dynamics equation and particle swarm optimization (PSO) algorithm thus studied the revolution of the ion track in CR39 during the etching process. The corresponding relationship between ion energy and track diameter and depth was obtained. It is found that when the ion range was equal to the etching depth in CR39, the track depth was the largest. The equation of the critical energy with which the track is the deepest and determined by the etching time was given.