In this paper, we study a single-item multi-stage remanufacturing inventory system using stochastic decomposition process. We extend the classic continuous inventory control policy to develop a control policy for this remanufacturing system. We use queuing theory techniques to derive steady-state probabilities and, consequently, the closed-form cost function of the remanufacturing system is estimated. A main contribution of this paper is providing a closed-form cost function for a multi-stage remanufacturing system which enables developing solution algorithm to find the optimal policy. Furthermore, a simulated annealing algorithm is proposed to find near optimal values of the inventory control policy parameters. Finally, sensitivity of the derived model to some parameters is analyzed.