The acoustic emission（AE） test of a concrete specimen subjected to uniaxial compression was carried out by CNC mechanical testing machine and SAEU2S digital acoustic emission system. The damage process in a concrete specimen was monitored by means of the propagating AE signal because of crack growth. The frequency spectrum character, energy change curve, AE counts, AE rate, and the relations between them and time were discussed in detail. The experiments show that the failure of concrete specimen is not instantaneous, but is such a transition from internal diffused microcracking to localised macrocracks and eventually to penetrating fracture. Acoustic emission can be detected in the whole process, whether that is emitted in the initial compaction and elastic deformation stage, or later in plastic deformation and penetrating fracture damage stage. In different stages the acoustic emission has significantly different characteristics. Based on this theory, a concrete structure stability acoustic emission warning system was designed. The results show that the system is able to correctly reflect the instability status of the concrete structure, and timely and accurately give warning information.