For large power dynamic load signals, firstly, this paper gives the amplitude modulation model of dynamic load voltage, current and power. Secondly, the characteristic functions and parameters of dynamic load signal run length and run probability distribution are defined. Based on this, the characteristics of the electric arc furnace current fundamental envelope signal and its run length probability distribution function and autocorrelation function are compared and analyzed. It shows that the two have similar characteristics. Then, the binary tour sequence of the current fundamental envelope signal is recovered from the stochastic process signal and compared with the stochastic process of the fundamental envelope of the actual dynamic load, it is verified that the dynamic load of the tour sequence can well represent the load characteristics. Finally, the conclusion of the analysis is summarized, and the parameters of the dynamic load signal model are proposed.