Abstract: With the increasing shortage of energy sources, extraction of shale gas is getting particularly urgent.Shale is tight and low-permeability, thus, stimulation treatment is necessarily needed to increase the reservoir permeability for commercialized production of the shale gas.Acidification pretreatment can effectively improve the shale pore structure and enhance the connectivity among shale pores, thus increases the shale permeability and gas production.In this experiment, the acidity treatment to the Niutitang formation shale samples are carried out under the mixture of hydrofluoric acid and hydrochloric acid, the mass fractions of which are 3% and 10% respectively.The evolution law of beddings, fractures, and pore structure on acidized shale samples for different durations are observed by an optical microscope.The trends of pores diameter, pore quantity, pore frequency and porosity of shale changing with time are summarized, and the influence of acidification on the shale gas flow is analyzed.Experimental results show that the brittle minerals in the shale of the Niutitang formation develop along bedding, and feldspar and quartz are strongly dissolved during the process of acidization, which can form fractures along the bedding; the exposed area of quartz and feldspar increase during the initial stage of acidization and decrease during the later stage of acidization, and at the later period of acidification, the pores between brittle minerals and other surrounding minerals enlarged obviously and are eroded deeply, which presentes a connecting tendency; according to the statistical characteristics of pores in the acidized shale, the acidification can be divided into two stages, new pores generation stage and pores enlargement stage; acidification transforms the structure of the shale samples from single-pore structure to a dual-medium structure made up with fissures and pores.While acidizing, the porosity of the shale samples increases at first and then decreases.The characteristics of the reservoir and the acid-rock reaction should be comprehensively considered in the production of shale gas to design an optimal operating time.