In order to study the mixed mode Ⅰ-Ⅱ fracture process of reinforced concrete， a grey and cusp catastrophe model was established based on the acoustic emission signals to identify thecritical mutation points of the fracture process. Meanwhile， the variations of energy release rate and ringing counting with time and 3D crack source locations were analyzed. The results show that some acoustic parameters， such as the energy release rate， increase abruptly in the conditions of crack at mid-span and critical load， and the grey and cusp catastrophe model based on ring counting rate can effectively distinguish the three critical conditions of mixed mode Ⅰ-Ⅱ fracture process like crack initiation at notch tip， crack at mid-span and critical load. There is a lot of internal damage near the bottom of the mid span during the mixed mode Ⅰ-Ⅱ fracture process. The conclusion can provide the basis for the stability analysis of concrete structure cracks and the establishment of early warning system.