Abstract: In order to study the current self-excited oscillation of electrochemical system which describes the diffusion of In(Ⅲ) in an electrolyte solution containing a large excess of sodium thiocyanate, the return maps and Poincare sections were adopted to investigate the dynamical state of mixed-mode oscillations and chaos. According to the simulation results, the mixed-mode oscillatory behavior for the typical oscillatory time series of the electric current had the form of a particular sequence, and the interjacent periodic states and chaotic states that were concatenation of the two principal states were displayed between two neighboring states. It was theoretically proved that the dynamical behavior of the electrochemical system had the characteristics of periodicity and complexity according to the bifurcation diagram and periodogram. The results indicated that the mixed-mode oscillations had the regular periodic changes which is the same as the results of the existing documents.