Abstract: In order to investigate the relationship between the macroscopic mechanical behavior and mesoscopic damage evolution characteristics of fiber reinforced geopolymer samples, a series of uniaxial compression tests were carried out on steel fiber reinforced fly ash geopolymer composites with different fiber volume contents (the volume ratios of fiber to mixture). Based on the acoustic emission technique, the acoustic emission behaviors during the compression process of samples were monitored. The influence of fiber volume contents on the failure behavior and the characteristics of acoustic emission of geopolymer under uniaxial compression was investigated. The results show that the strength, ductility, the increasing slope and average frequency of acoustic emission waveform increase as the fiber content increases, and the failure mode of the samples changes from brittle catastrophic pattern to ductile pattern gradually. In the earlier stage of destruction, the acoustic emission hit rate and energy release rate (abbreviate energy rate) of samples with the fiber volume content of 0 or 0.5% maintain a higher level, and finally leads to the catastrophic rupture of the samples. However, the fiber volume content of 2.0% makes the acoustic emission hit rate and the energy rate reach the peak at the inflection point of stress-time curve, and then decrease slowly, leads to the ductile rupture of samples finally. Therefore, predicting the occurring of catastrophic rupture depends on the rapid increasing of acoustic emission hit rate or energy rate simply, may gives false information sometimes.