This paper introduces an improved BCI system based on alpha rhythm, the main composition units of the system are electrodes, acquisition circuit, online detecting algorithm and outer devices. For improving the performance of BCT systems, a new algorithms for alpha wave detection is proposed, which can reduce EEG baseline wandering and energy fluctuation efficiently and make the BCI system work more stable. Based on the BCI system, experiments of media player control are carried out among different subjects, which show that the system has an excellent performance in alpha wave detection and real-time controlling.