Nowadays, energy conservation is one of the most talked about issues in our life, it is also increasingly important in dynamic flexible flow shop scheduling problems. Previous research did much on how to minimize total earliness and tardiness of all jobs, or to achieve just-in-time production, whereas little effort has been made on how to save energy. Therefore, to address such need, a dynamic machine switching method has been proposed in this paper. The main purpose is to minimize both energy consumption and just-in-time production objectives. Featured by switching machines dynamically, the proposed method has been tested on different environments, whose results show that it has good performance for energy conservation.