Abstract: The chaotic leader is different from stepped leader and dart leader with distinctive features. It has many narrow pulses, causing strong high-frequency radiation. The pulse occurs right at the position of preceding stepped leader and dart leader, but its structure, width and interval all show significant irregularities. The chaotic leader is a new and special one with no exact definition of its pulse characterization so far.Multi-scale entropy is applied to the analysis of chaotic leader, and some key parameters applying in the lightning irregular pulse signal analysis are given after detailed analysis. Dart leader signal, stepped leader signal and the chaotic leader signal are analyzed with the given method and the results are compared, and case studies of the three-leader multi-scale entropy features prove the feasibility of this method. It's found out through statistical analysis that 3 leaders are different in entropy value especially when the scale is greater than 3, and thus they can be clearly distinguished by entropy values. Entropy value greater than 1.5 may indicate chaotic leader, and entropy value less than 1.5 is classified as stepped leader or dart leader. Furthermore chaotic leader and dart leader entropy value both increase with scales first and then stabilize but stepped leader entropy value doesn't change much. Characteristic entropy values for the chaotic leader are given: The average is about 2.0—2.1, the maximum is 2.6—2.8, and the minimum is 1.51—1.59. Based on the analysis of multi-scale entropy characteristics of 3 leaders, the physical meaning of the irregularity is also discussed. The irregularity degree of chaotic electric field pulse can be reflected by the entropy value: The greater the entropy value is, the greater the degree of irregularity. The characteristics of the electric field pulse in the waveform is directly related with the development of the discharge process. For the dart leader or stepped leader, the smaller entropy value illustrates that its discharge is regular. The chaotic leader in small scale with larger entropy directly demonstrates that in this range scale its discharge, polarity and intensity are irregular. It shows the electric discontinuity somewhere in the leader development channel during a certain period before the occurrence of subsequent stroke.