The bending mechanical mechanism of ARB(accumulative roll bonding) specimen was studied. Based on macro-micro plastic theory, theoretical model of the limiting bending load of ARB specimen was established every cycle. Through comparing with the experiment of the reference, this model was verified. Moreover, based on reliability analysis method, considering the randomness of the grains and the dislocation, theoretical model of standard deviation of limiting bending load of ARB specimen was established. Furthermore, the critical curve theoretical model of plastic zone of ARB specimen was established every cycle. Based on this model, the plastic zone of ARB specimen every cycle was discussed. The study in the paper provides analysis method and theory foundation for bending mechanical mechanism of ARB specimen.