Abstract: From the perspective of demands that follow a phase distribution, a supply chain that contains a manufacturer and several retailers is studied. It was modeled into a Markov process. Then, by analyzing the transition relationship of all the states of the supply chain, an expression of the transfer matrix about the states of manufacturer and three retailers is given. And the expressions for calculating the probability of out of stock and full stock of the retailers in all the different phases are given. So the theoretical basis is given for coordination and control of the supply chain. Numerical experiments explain the regularity of change of the retailers service level with the change in different demands.