Abstract：Based on the results of triaxial cyclic on/off loading experiment using the same sample treated by multiple acid，the influence of acid treatment on deformation feature of rock has been analyzed specifically. The results show acid treatment and the quantity of acid flooding have significant effect on deformation of rock. The effect of the acid flooding for the first time is obvious，and the elastic modulus and Poisson’s ratio decrease dramatically in the process loading/unloading. However，the effect is tapering off when the quantity of acid flooding is large enough because of decrease of the lyotrope and dissoluble mineral. Elastic modulus in the process of loading/unloading is decreasing with the increasing of multiple acid treatments，so is the Poisson’s ratio. The changes of elastic modulus and Poisson’s ratio in the early stage are greater，and tend to smooth in the later stage. And the regularity of Poisson’s ratio in the process of loading/unloading is indistinct. When the clyclic load reaches to the maximum value，the axial deformation is increasing gradually with the increasing of quantity of acid flooding. Therefore，acid treatment is one of the important factors that affect the mechanical deformation behavior of rock. In the gas and oil industry，the alternation of loading capacity of rock treated by acid and the negative impacts in the later engineering operation should be noticed.
