To alleviate the growing concern of energy waste in networked devices, we propose an energy saving strategy in the "server-centric" data center network. Focusing on servers, we introduce a basic scheme based on the transition of automata. By changing efficiently from sleeping state to active state in different network traffic, servers save the energy. This scheme is self-adaptive and simple. Based on this prime scheme, we enhance the strategy by further taking advantage of the unique topology of BCube. We present a structure algorithm relying on the active substructure in BCube. Combining with the basic scheme and structure algorithm, our energy saving strategy can achieve a high proportion of energy saving without sacrificing service quality like packet delay in the simulation with real traffic trace.