To address the microgrid with several kinds of Distributed Energy Resources (DERs), this paper proposes a decentralized method for solving its Dynamic Economic Dispatch (DED) problem based on distributed simplex method. By leveraging linearization of the objective function, DED problem is converted into a linear programing model. Regarding each DER as an individual agent, the cost vector and constraints coefficient matrix in this model can be partitioned into blocks according to agents. This is convenient to use the distributed simplex method to solve it. During iterations, each agent exchanges the optimal basis and corresponding cost vector with its neighbors through a communication network. Without the participation of the central controller, the privacy information of agents can be protected effectively, and the number of communication rounds grows linearly with the diameter of communication network. Simulation on a real microgrid verifies the accuracy of the linearized model, and demonstrates the effectiveness of the proposed approach. This work is supported by National Key Basic Research and Development Program of China (973 Program) (No. 2013CB228205).