  To describe and analyze the dynamics of Self-Organized Criticality (SOC)
systems, a four-state continuous-time Markov model is proposed in this paper.
Different to computer simulation or numeric experimental approaches commonly
employed for explaining the power law in SOC, in this paper, based on this
Markov model, using E.T.Jayness' Maximum Entropy method, we have derived a
mathematical proof on the power law distribution for the size of these events.
Both this Makov model and the mathematical proof on power law present a new
angle on the universality of power law distributions, they also show that the
scale free property exists not necessary only in SOC system, but in a class of
dynamical systems which can be modelled by the proposed Markov model.
