Only a few mature techniques can estimate the mechanical damage of concrete,but they cannot offer a real-time judgement for structural state, acoustic emission (AE) technology was presented to monitor its damage evolution under three point bending testing. The cement mortar damage evolution law was studied applying the AE characteristic parameter time series fractal theory. The acoustic emission fractal features of all stress levels in the whole cement mortar failure and the changing rules of fractal value were studied. The results show that, in the initial and middle stage of loading,the fractal value of cement mortar is unsteady;When the cement mortar crack begins its fast propagation, the fractal dimension appears the “increase-decrease” pattern, which can be used to identify the cement mortar critical failure.